Grade 12 - Comp. / Discrete laws 60 exercises (including 59 corrected)

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1. Reminders: probabilities E.7117 The table below provides an overview of daily newspaper readership in France, based on a sample of 800 people surveyed in 2005 . Every day or almost every day Once or twice a week Only-during certain periods Rarely Never Total Farmers operators 1 10 2 8 79 100 Craftsmen, shopkeepers , business leaders 11 11 5 7 66 100 Managers 17 16 10 18 39 100 Intermediate professions Media 8 15 7 15 55 100 Employees 6 7 4 9 74 100 Workers (including agricultural workers) 4 5 3 5 83 100 Retired 6 7 2 6 79 100 Others inactive 5 9 4 9 73 100 Total in workforce 58 80 37 77 548 800 Percentages of total 7.25 % 10 % 4.625 % In this exercise, the results will be given in decimal form and rounded to the nearest 0.001 . Part A. 1 The last row of the table below shows the share of each category in relation to the total sample. Calculate the missing values in this last row. 2 Give the probability that a person chosen at random from among the executives never reads. Part B. A person is chosen at random from this sample of 800 people. In this section, we note the following events : J Event : ˇ The person chosen never reads ı ; O Event : ˇ The person chosen is a laborer ı. 1 Calculate the probabilities of events J and O 2 Calculate the probability of event J O . 3 Calculate the probability of event J O E.7118 Let Ω ; P be a probabilized space where A and B are two events of Ω such that : P ( A ) = 0.36 ; P ( B ) = 0.27 1 What can we say about A and B if P A B =0.63 ? 2 Assume : P A B =0.5 : a What can we say about A and B ? b What is the probability of an event simultaneously re-alizing the events A and B ? E.7119 The works council of a Parisian company wants to organize a weekend trip to the provinces. A survey is conducted among the 1 200 employees of this com-pany to find out their choice of transportation. (The only means of transportation offered are train, plane, or bus.) . The results of the survey of company employees are listed in the following table : Train Plane Coach Total Women 468 196 56 720 Men 150 266 64 480 Total 618 462 120 1200 An employee of this company is interviewed at random (it is assumed that all employees have the same chance of being interviewed) . F the event : ˇ the employee is a woman ı ; T the event : ˇ the employee chooses the train ı. 1 Calculate the probabilities P ( F ) , P ( T ) then determine the probability that the employee will not choose the train (the results will be given in decimal form) 2 a Determine the probability of the event F T . b Deduce the probability of the event F T . 3 By choosing an employee at random from among the em-ployees who did not choose the train, what is the proba-bility that this employee is a woman? (The result will be rounded to three decimal places) 2. Reminders: probability law E.7120 Let X be a random variable whose prob-ability distribution is given below : x i 1 2 3 4 5 6 P X = x i 0 ; 05 0.12 0.15 0.23 0.17 a 1 Determine the value of a so that the table below repre-sents a probability distribution. 2 Determine the following probabilities : a P X 3 b P X < 5 https://chingmath.fr chapExoCorrec/7117 sacados/7117 chapExoCorrec/7118 sacados/7118 chapExoCorrec/7119 sacados/7119 chapExoCorrec/7120 sacados/7120
SESESESESESESE SESESESESESESESESESESESESESESE V3F3V2V3F3F2V1V3F3V2V3F3F2F1 3. Reminders: binomial distribution E.7155 Here are the choice trees associated with repeating a Bernoulli test 3 and 4 times respectively: 1 For the threefold repetition of Bernoulli’s test, complete the table below : Number of succès 0 1 2 3 Number of issues 2 For the four-fold repetition of Bernoulli’s test, complete the table below : Number of succès 0 1 2 3 4 Number of issues E.7121 A MCQ (multiple-choice questionnaire) is given to students : it contains three questions, and for each question, four answers are provided, only one of which is cor-rect. We want to study the success rate for this multiple-choice questionnaire if students answer completely at random ; we therefore assume that the answers given to each question are independent of each other. We note : F i : ˇ The answer given to question i is false ı ; V i : ˇ The answer given to question i is true ı ; 1 Complete the weighted tree below : 2 Let X be the random variable that associates each ele-mentary event with the number of correct answers ob-tained in the multiple-choice test. a Justify that the random variable X follows a binomial distribution with parameters 3 and 0.25 . b In order to obtain the probability distribution of the random variable X , complete the table below : k 0 1 2 3 P X = k c Calculate the expected value of the random variable X . E.7168 Reminder : for a random variable X following a binomial distribution with parameters n and p , the probability that the random variable takes the value k is : P X = k = n k · p k · 1 p n k Note: the binomial coefficient n k allows us to know the number of paths in the decision tree result-ing in k successes for n repetitions. Above is a screenshot of a calculator for calculating the bi-nomial coefficient 5 3 . 1 Using the calculator, determine the binomial coefficients below : a 5 3 b 4 0 c 4 2 d 7 5 2 Consider the random variable X following the binomial distribution with parameter B 12 ; 0 ; 3 . Determine the following probabilities rounded to 10 4 : a P X =3 a P X =7 3 Consider the random variable X following the binomial distribution with parameter B 8 ; 0 ; 4 . Determine the following probabilities using the complementary distri-bution, rounded to 10 4 : a P X 1 a P X 7 E.7169 Results are rounded to the nearest 10 3 . In a watch factory, when the production machines are prop-erly adjusted, 4 % of the watches produced are defective. To check the state of production, 10 watches are drawn suc-cessively, at random and independently of each other. The random variable associates the number of defective watches with this draw. 1 Justify that the random variable X follows a binomial distribution. Specify its parameters. 2 What is the probability that at least 1 watch is defective? We’ll round the value to the nearest 10 4 . 4. Non-symmetrical tree https://chingmath.fr chapExoCorrec/7155 sacados/7155 SESESESESESESE SESESESESESESESESESESESESESESE chapExoCorrec/7121 sacados/7121 V3F3V2V3F3F2V1V3F3V2V3F3F2F1 chapExoCorrec/7168 sacados/7168 chapExoCorrec/7169 sacados/7169
::::::AG::::::A:::AG ALE0;550;37ALGE E.7133 A company was interested in the probability of one of its employees, chosen at random, being absent during a given week of winter 2014 . The probability of an employee having the flu in a given week was estimated to be 0.07 . If the employee has the flu, then he or she is absent. If the employee does not have the flu that week, the probabil-ity that he or she will be absent is estimated at 0.04 . An employee of the company is chosen at random and the following events are considered : G : the employee has the flu in a given week; A : the employee is absent in a given week. 1 Reproduce and complete the tree, indicating the proba-bilities of each branch. 2 Show that the probability p ( A ) of the event A is equal to 0.1072 . E.7216 In January 2015 , the director of a contemporary art museum commissions a survey on visitor habits. The museum has a website. To purchase a ticket, interested individuals can go to the museum ticket office or order a ticket online. Three types of visits are available: Individual visits without an audio guide. Individual visits with an audio guide. Group visits for at least 10 people. In this case, a single ticket is issued for the group. The website only allows you to purchase individual tickets with or without an audio guide. For group visits, you must go to the museum ticket office. Over the course of the year 2015 , the survey revealed that : 55 % of admission tickets were purchased at the museum ticket office ; of the tickets purchased at the museum ticket office, 51 % were for individual visits without audio guide rental, and 37 % were for visits with audio guide rental; 70 % of the tickets purchased online correspond to indi-vidual visits without audio guide rental. We randomly select a museum ticket purchased on 2015 We consider the following events : E : ˇ the ticket was purchased online ı ; A : ˇ the ticket is for an individual visit with audio guide rental ı ; L : ˇ the ticket corresponds to an individual visit without audio guide rental ı ; G : ˇ the ticket corresponds to a group visit ı Remember that if E and F are two events, p ( E ) denotes the probability of event E and p F ( E ) denotes the probability of event E given that event F has occurred. We denote E as the opposite event of E . 1 Copy and complete the following weighted tree represent-ing the situation described in the statement : 2 Show that the probability that the ticket was purchased online and corresponds to an individual visit with audio guide rental is equal to 0.135 . 3 Show that : p ( A ) = 0.3385 4 The ticket chosen corresponds to an individual visit with audio guide rental. What is the probability that this ticket was purchased at the museum ticket office? The result will be rounded to the nearest thousandth 5. Conditional probability and binomial distribution E.7136 A large company has just com-pleted its recruitment campaign, which took place in two stages : first stage : review of the candidate’s application ; second stage : interview for recruitment purposes. The recruitment process implemented by the company is as follows : if the application is deemed to be of good quality, the candidate is invited to an interview with the human re-sources director ; if the application is not deemed to be of good quality, the candidate undergoes tests and is then invited to an interview with the company director. In both cases, at the end of the interview, the candidate is either hired or not. By choosing a candidate at random, we construct a random experiment whose probability tree is represented below with some of the data retrieved from the publication : https://chingmath.fr chapExoCorrec/7133 sacados/7133 ::::::AG::::::A:::AG chapExoCorrec/7216 sacados/7216 ALE0;550;37ALGE chapExoCorrec/7136 sacados/7136
0;3:::RPDR0;24:::RD0;7:::RPDR::::::RD 0;950;7S0;3SR0;050;2S0;8SR where D is the event ˇ the candidate has a file that is consid-ered to be of good quality ı ı and R is the event " the candidate is hired by the company ı. 1 a Determine the probability P D R . b Furthermore, we know that 38 % candidates were hired. Deduce the probability P D R . c Complete the probability tree 2 Ten people apply for a job at the company. Their ap-plications are reviewed independently of each other. Let X be the random variable giving the number of people recruited from among the 10 applicants. a Justify that X follows a binomial distribution with pa-rameters n =10 and p =0.38 . b Calculate the probability that at least one of the ten people will be hired. Give the exact value, then a value rounded to 10 3 . E.7139 A survey was conducted among students enrolled in a high school lunch program. The results were used to construct the probability tree below : A student is chosen at random from among those enrolled in the lunch program. We note the following events : R the event : ˇ the student regularly eats in the cafete-ria ı ; S the event : ˇ the student is satisfied ı. We note R and S as the opposite events of R and S . 1 a Show that the probability of event S is equal to 0.675 . b Knowing that the student is not satisfied with the qual-ity of the meals, calculate the probability that he eats regularly in the cafeteria. Give the result rounded to 10 3 . 2 Four students are randomly selected from among those enrolled in the half-board program and questioned suc-cessively and independently. Let X be the random variable equal to the number of students who say they are satisfied with the quality of the meals. Since the number of students is large enough, we consider that X follows a binomial distribution. The results will be rounded to three decimal places. a Specify the parameters of this binomial distribution b Calculate the probability of event A : ˇ all four students are satisfied with the quality of the meals ı. c Describe event A in one sentence and calculate its prob-ability. https://chingmath.fr 0;3:::RPDR0;24:::RD0;7:::RPDR::::::RD chapExoCorrec/7139 sacados/7139 0;950;7S0;3SR0;050;2S0;8SR
0;650;3E0;7EH0;350;6E0;4EF E.7217 A mobile phone operator is orga-nizing a telephone marketing campaign to offer its customers a new subscription plan. Some of the people contacted listen to the explanation, while others hang up immediately (or say they are not interested) . A person is chosen at random from the customer database. Each person has the same probability of being chosen. We denote H the event ˇ the person chosen is a man ı, F the event ˇ the person chosen is a woman ı, E the event " the person chosen listens to the salesperson’s explanations ı and E the opposite event of E . Reminder of notation: If A and B are two given events, P ( A ) denotes the probabil-ity that event A will occur and P B A denotes the probabil-ity of event A occurring, given that event B has occurred. Part A The study has established the following probability tree : For each statement, only one of the answers is correct. Copy the number of the answer and the value chosen onto your answer sheet. No justification is required 1 The probability that the person chosen will listen to the salesperson’s explanations is equal to : a 0 ; 195 b 0 ; 21 c 0 ; 405 d 0 ; 595 2 The salesperson addresses a person who listens to them. The probability, rounded to two decimal places, that this person is a man is equal to : a 0 ; 48 b 0 ; 52 c 0 ; 76 d 0 ; 24 Part B The surveys conducted during these first few days also show that 12 % of those interviewed subscribe to this new package. Each employee of the operator makes 60 calls per day. We assume that the file is large enough for the choices to be considered independent and made under identical conditions. Let X be the random variable that counts the number of sub-scriptions made by a given employee on a given day. 1 Justify that the random variable X follows a binomial distribution, the parameters of which will be given. 2 Determine the probability that the employee will obtain 5 subscriptions on a given day. (The result will be rounded to two decimal places.) 3 Determine the probability that the employee will obtain at least one subscription on a given day. (The value will be rounded to the nearest ten-thousandth) . E.7312 A survey was carried out among students at a high school to find out their views on the length of the lunch break and school rhythms. The survey revealed that 56.75 % of the school’s students were in favor of spread-ing classes out over the school year. Four students taken at random from among the school’s pupils are interviewed successively and independently. Let X be the random variable that gives the number of students in favor of a more staggered distribution of classes over the school year. As the number of students is sufficiently large, X is considered to follow a binomial distribution. 1 Specify the parameters of this binomial distribution. Results will be rounded to the nearest 10 4 . 2 Calculate the probability that none of the four students surveyed is in favor of spreading classes out more over the school year. 3 Calculate the probability that exactly two students are in favor of a more spread-out course distribution over the school year. E.7137 A large company has just com-pleted its recruitment campaign, which took place in two stages : first stage : review of the candidate’s application ; second stage : interview for recruitment purposes. The recruitment process implemented by the company is as follows : if the application is deemed to be of good quality, the candidate is invited to an interview with the human re-sources director ; if the application is not deemed to be of good quality, the candidate undergoes tests and is then invited to an interview with the company director. In both cases, at the end of the interview, the candidate is either hired or not. At the end of this recruitment campaign, the company pub-lishes the following results : 30 % of the candidates had applications that were deemed to be of good quality; 20 % candidates whose applications were not considered to be of good quality were recruited ; 38 % candidates were recruited. 1 We take a random candidate and note : D the event ˇ the candidate has a file that is considered to be of good quality ı ; R the event ˇ the candidate is hired by the company ı. a Represent this situation using a weighted tree b Calculate the probability that the candidate does not have a good application and is not hired by the com-pany. c Show that the probability of event D R is equal to 0.24 . d Deduce the probability that a candidate will be hired given that their application is considered to be of good quality. Complete the weighted tree created in ques- https://chingmath.fr chapExoCorrec/7217 sacados/7217 0;650;3E0;7EH0;350;6E0;4EF chapExoCorrec/7312 sacados/7312 chapExoCorrec/7137 sacados/7137 Extrait de Centres Etrangers Juin 2014
EvènementsélémentairesNNNNNNNBBNNNNNNNNBBNBNNBNNBBBB1ertirage2etirage 3XV2F2F2FV2V1F1F1FF2V1F1F1FF2V1F1F1FFV2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF tion a . 2 Ten people apply for a job at the company. Their ap-plications are reviewed independently of each other. Let X be the random variable giving the number of people hired among the 10 applicants. a Justify that X follows a binomial distribution with pa-rameters n =10 and p =0.38 . b Calculate the probability that at least one of the ten people will be hired. Give the exact value, then a value rounded to 10 3 . 6. Independent repetition of identical experiments E.7683 Consider a random experiment with two outcomes : S success and E failure. These two outcomes are equiprobable. We repeat this experiment 4 times independently. The choice tree below is used to describe this repetition: 1 How many different outcomes does this random experi-ment have? 2 Determine the probability of obtaining 4 success. 3 a How many outcomes represent 3 success? b Determine the probability of obtaining 3 success in this random experiment. E.7423 An urn contains two black balls and one white ball; the game is played with the ball being re-turned : i.e., once the ball has been drawn, it is returned to the urn before the next draw. Here’s a decision tree based on the drawing of two balls : 1 Taking into account the order in which the balls are drawn, what is the possible number of different draws? 2 Determine the probability of the following events : a A : ˇ The first ball drawn is blanche ı. b B : ˇ The two balls drawn are différentes ı colors. c C : ˇ The second ball is a noire ı ball. 3 Give the probabilities of the following events : a A B b B c C 7. Independent repetition of identical experiments and random variables E.7386 Consider a multiple-choice question-naire consisting of 3 questions each offering 4 answers, only one of which is correct. A random experiment is created by asking participants to randomly answer the questions proposed in the form. This situation is represented by the choice tree below : https://chingmath.fr chapExoCorrec/7683 sacados/7683 chapExoCorrec/7423 sacados/7423 EvènementsélémentairesNNNNNNNBBNNNNNNNNBBNBNNBNNBBBB1ertirage2etirage chapExoCorrec/7386 sacados/7386 3XV2F2F2FV2V1F1F1FF2V1F1F1FF2V1F1F1FFV2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF
EvènementsélémentairesNNNNNNNNBNNBNNNNNNNNNBNNBNNNBNNNBNBNBBBNNNNNNNNNBNNBNNNNNNNNNBNNBNNNBNNNBNBNBBBNNBNNNBNNBBNBNNBNNNBNNBBNBNNBBNNBBNBBBBBB V3F3V2V3F3F2V1V3F3V2V3F3F2F1 For each elementary event, the random variable X is associ-ated with the number of correct answers. Give the probability distribution of the random variable X . E.5169 There are three balls in an urn : two black balls and one white ball. Three balls are drawn succes-sively from this urn, with replacement. The decision tree below illustrates all the elementary events of this random experiment : Each draw is associated with a payoff as follows : 0 e if no black balls are drawn ; 1 e if only one black ball is drawn ; 2 e if two black balls are drawn ; 5 e if all three balls are black. We consider the random variable X which associates each draw with the corresponding prize. Complete the table below giving the distribution of the ran-dom variable X : k 0 1 2 5 P X = k 8. Expectations, variances and independent repetition of identical experiments E.5190 A QCM (multiple-choice question-naire) is proposed to students : it com-prises three questions and for each of these questions, four answers are pro-posed, of which only one is correct. We wish to study the percentage of success in this MCQ if the students answer it completely at random ; we then assume that the answers given to each of the questions are independent of each other. We note : F i : ˇ The answer provided to question i is fausse ı ; V i : ˇ The answer provided to the question i is vraie ı ; 1 Complete the weighted tree shown above. 2 We note X the random variable counting the number of correct answers provided to the MCQ. a Determine the probability distribution of the random variable X . b Calculate the expectation of the random variable X . E.5913 A company produces electronic components before êbeing as-signed to sales. Each component undergoes two independent quality tests : 5 % of the components fail the first test ; 3 % of the components fail the second test. At the end of the production line, an electronic component is chosen at random.î 1 Determine the probability that the electronic component failed both tests. 0.0012 0.0013 0.0014 0.0015 2 Determine the probability that the electronic component failed only one of the two tests. 0.0666 0.077 0.0776 0.078 3 The coût of production is calculated as follows : each component coûte 100 e and for each failed test, the re-pair coûte 10 e . Let X be the random variable that associates each ran-domly selected component with its production cost coût. What is the expected value of the random variable X ? 100.8 101.8 102.8 103.8 https://chingmath.fr chapExoCorrec/5169 sacados/5169 EvènementsélémentairesNNNNNNNNBNNBNNNNNNNNNBNNBNNNBNNNBNBNBBBNNNNNNNNNBNNBNNNNNNNNNBNNBNNNBNNNBNBNBBBNNBNNNBNNBBNBNNBNNNBNNBBNBNNBBNNBBNBBBBBB chapExoCorrec/5190 sacados/5190 V3F3V2V3F3F2V1V3F3V2V3F3F2F1 chapExoCorrec/5913 sacados/5913
Urne AUrne B123 P(CP(PPP(PPCP(CP(PPP(PPC ::::::R:::VB::::::R:::VN E.5914 A company manufactures electronic components. During pro-duction, each component undergoes two quality tests. If, during one of the tests,ôthe test is negative, the component is repaired and returned to the production line. 6 % of components fail the first test. ; 2 % of components fail the second test. At the end of the production line, an electronic component is chosen at random.î 1 Determine the probability that the electronic component failed both tests. 0.0012 0.0013 0.0014 0.0015 2 Determine the probability that the electronic component failed only one of the two tests. 0.0666 0.077 0.0776 0.078 3 The coût of production is calculated as follows : each component coûte 100 e and for each failed test, the re-pair coûte 10 e . Let X be the random variable that associates each ran-domly selected component with its production cost coût. What is the expected value of the random variable X ? 100.8 101.8 102.8 103.8 9. Independent succession of random experiments E.5915 Consider two urns A and B contain-ing four and three objects respectively as shown below : The game consists of drawing an object from urn A then from urn B : 1 How many different pairs of objects can be obtained from the two draws? 2 Consider the following two events : C : ˇ The pair of objects includes a carré ı P : ˇ the pair of objects includes a pentagone ı Determine the following probabilities : a P ( C P ) b P ( C P ) c P ( C P ) d P ( C P ) 3 a Determine the following two probabilities : P ( C ) ; P ( P ) b Copy and complete the tree below with the probabilities shown : c Can we find the results of ques-tion 2 using the probability tree from the previous question. E.5191 Two urns A and B are available, each containing balls indistinguishable by touch. Here is the composition of the urns : Urn A : three black balls and two white balls ; Urn B : five red balls and two green balls. One ball is drawn successively from each of the urns. Consider the following events : B : ˇ the ball drawn is blanche ı ; N : ˇ the ball drawn is noire ı ; R : ˇ the ball drawn is rouge ı ; V : ˇ the ball drawn is verte ı. 1 Copy and complete the probability tree below : 2 Determine the value of the following probabilities : a P ( B R ) b P ( B V ) c P ( N R ) 3 a Give the value of : P ( B R )+ P ( N R ) . b What do we notice? https://chingmath.fr chapExoCorrec/5914 sacados/5914 chapExoCorrec/5915 sacados/5915 Urne AUrne B123 P(CP(PPP(PPCP(CP(PPP(PPC chapExoCorrec/5191 sacados/5191 ::::::R:::VB::::::R:::VN
CBA ABACACABA E.5168 A small restaurant offers three main courses and two desserts on its menu. Here is a description of the menu : Spaghetti . . . . . . .6 e Beef fillet . . . . . . .7 e Rib steak . . . . . . .8 e Fruit salad . . . . . . . .2 e Custard . . . . . . . . . . 3 e Each customer entering the restaurant orders exactly one main course and one dessert. 1 Taking a random customer leaving the restaurant, spec-ify what their bill might be. 2 Assuming that all combinations main course = dessert have the same probability of being chosen by a customer. a How many combinations can be created from this menu? b What is the probability that a customer paid 8 e ? 11 e ? c Show that the probability of having a bill for 10 e is 1 3 . d Complete the table below : Invoice amount 8 9 10 11 Probability E.5350 A tourist travels for two days to the Pacific coast of Mexico in the locality of ˇ Faro de Bucerias ı. On the way to the beach, two paths are offered to the beaches of ˇ Maruata ı and ˇ Playa Ventura ı. On the first day, the tourist chooses one of the two beaches at random. On the second day, he will change beaches with probability 3 4 . What is the probability that the tourist has been to the beach ˇ Playa Ventura ı at least once? E.6633 An elephant moves to three points in its territory. It starts at point A and makes three moves : Either, he turns clockwise with 2 chances out of three other-wise, he moves counterclockwise. It is assumed that each of his moves is independent of the previous ones. What is the probability that, at the end of these moves, he will arrive at the point B ? 10. Random variables and repetitions of independent experiments E.133 lebanon - 2004 - choice - 7 points In an animal experiment, a rat is placed at the start of a run and asked to choose one of 3 exit doors : if it borrows the door A , it goes out if he borrows one of the doors B or C , he is brought back to the start, and this until he chooses the door A . We’ll give the results as irreducible fractions Part A : It is assumed that the rat has no memory: it chooses a door at random and can borrow the same door several times in a row. Each door therefore has the same probability of being chosen. 1 What is the probability that it will come out on the first try? 2 What is the probability that he only comes out on the second try (the first being missed and the second being successful) ? 3 What is the probability that it only comes out on the fourth try? Part B: It is assumed that the rat has a perfect memory: at each step, it randomly chooses one of the doors it has never been through. 1 On the appendix below (return with copy) , complete the tree with the weightings. 2 X denotes the number of trials it takes to exit. What values can the number X take? 3 Complete the table below : Value of X 1 2 3 Probability 1 3 https://chingmath.fr chapExoCorrec/5168 sacados/5168 chapExoCorrec/5350 sacados/5350 chapExoCorrec/6633 sacados/6633 CBA sacados/133 Liban - 2004 - au choix - 7 points ABACACABA
V3F3V2V3F3F2V1V3F3V2V3F3F2F1 -1-22 112 E.4797 A balanced die has letters written on its faces : two A , two B and two C . The random experiment consists of rolling the die three times and noting, each time, the letter of the hidden face. Thus, at each output of the random experiment, a three-letter word is constructed. 1 Describe the 27 mots that can be obtained in this random experiment. It is assumed that each of these words has the same probabil-ity of exit. 2 Give the probability of the following events : a A : ˇ Le word obtained contains exactly once the letter B ı ; b B : ˇ The word obtained contains exactly twice the let-ter B ı ; c C : ˇ The word contains the same letter in the first and third place ı. 3 Based on the construction of these words, we have cre-ated a new game with the following rules : The player wins 2 e if the word contains the letter only once B ; the player wins 5 e if the word contains exactly two instances of the letter B . The player wins 10 e if the word is ˇ BBB ı. We note ˇ X = k ı the event ˇ the player wins k e ı. Com-plete the table below : k 0 2 5 10 P ( X = k ) 11. Random variables, expectations, standard deviations and repetitions E.4811 A QCM (multiple-choice questionnaire) is proposed to students : it comprises three questions and four answers are proposed, only one of which is correct. We wish to study the percentage of success in this MCQ if the students answer it completely at random ; we then assume that the answers given to each of the questions are indepen-dent of each other. We note : F i : ˇ The answer provided to question i is fausse ı ; V i : ˇ The answer provided to the question i is vraie ı ; 1 Complete the probability tree below : 2 Note X the random variable counting the number of cor-rect answers provided to the MCQ. a Determine the probability distribution of the random variable X . b Calculate the expectation of the random variable X . E.7501 An urn contains three balls indistin-guishable to the touch bearing the num-bers 2 , 1 and 2 . Consider the random experiment of suc-cessively drawing a ball from the urn three times and putting it back each time. Consider the random variable X which associates with each experiment, the sum of the numbers obtained on the balls drawn. Determine the expectation of the random variable X Any trace of research or initiative, however incomplete, will be taken into account in the assessment. E.7562 An urn contains three balls indistin-guishable to the touch bearing the num-bers 1 , 1 and 2 . Consider the random experiment of suc-cessively drawing a ball from the urn three times and putting it back each time. Consider the random variable X which associates with each experiment, the sum of the numbers obtained on the balls drawn. Determine the expectation of the random variable X Any trace of research or initiative, however incomplete, will be taken into account in the assessment. https://chingmath.fr chapExoCorrec/4797 sacados/4797 chapExoCorrec/4811 sacados/4811 V3F3V2V3F3F2V1V3F3V2V3F3F2F1 chapExoCorrec/7501 sacados/7501 -1-22 chapExoCorrec/7562 sacados/7562 112
E.5196 A chocolate factory produces boxes of chocolates each year, including 50 % with milk chocolate, 30 % with dark chocolate, and 20 % with white chocolate. 70 % of the boxes contain plain chocolates, while the others contain chocolates filled with caramel. These proportions are independent of the type of chocolate used to make the box. Consider the following events : L : ˇ milk chocolate is used ı ; N : ˇ dark chocolate is used ı ; B : ˇ white chocolate is used ı ; Na : ˇ the chocolates are plain ı ; C : ˇ the chocolates are filled with caramel ı ; All results will be given in decimal form. 1 Draw the weighted tree associated with this situation. 2 A box is chosen at random from the factory output. De-termine the probabilities of the following events : a ˇ the box contains dark and natures ı chocolates. b ˇ the box contains dark or plain chocolates ı 3 The company sets box prices as follows : le base price for a box of chocolate is 9 e ; if the chocolate used is dark chocolate then the price is increased by 4 e ; if the chocolate used is white chocolate then the price is increased by 2 e ; if the chocolates are caramel-filled, the price per box increases by 2 e . The random variable X associates a box produced by the factory with its belly price. a Draw the table representing the probability distribu- tion associated with the random variable X . b Determine the expectation of the random variable X round to the nearest tenth. E.6631 A nursery offers three types of trees : acacias, plane trees, and oaks. Each of these trees can be pur-chased in different sizes : either as a ˇ young sapling ı ( 0.75 meters) , or as an ˇ mature tree ı ( 2 meters) . At the âsapling stage, acacias, plane trees, and oaks are worth 50 e , 65 e and 80 e respectively. If the customer wants to buy the adult form, they must add 15 e . In his end-of-year review, he notes that 40 % of the trees sold are oaks and that acacias and plane trees share the remaining sales equally. He also notices that, regardless of the type of tree, a quarter of sales are always made on " adult ı. The random experiment considered consists of randomly drawing an invoice from the financial year 2015 . The following events are considered : A : ˇ The tree purchased is a acacia ı P : ˇ The tree purchased is a platane ı C : ˇ The tree purchased is a chêne ı J : ˇ The tree is a sapling ı 1 Draw a weighted tree representing this situation 2 Consider the random variable X associating the invoice drawn with its amount. a Draw the table of the probability distribution of the random variable X . b Calculer the expectation of the random variable X . c Donner the standard deviation of X to the nearest tenth. 12. Random variables, expectations, standard deviations and conditional proba-bilities E.4890 A chocolate factory produces boxes of chocolate throughout the year, of which 50 % are made with milk chocolate, 30 % with dark chocolate, and 20 % with white chocolate. 70 % of the boxes contain plain chocolates, while the others contain caramel-filled chocolates. These proportions are inde-pendent of the type of chocolate used to make the box. Consider the following events : L : ˇ milk chocolate is used ı ; N : ˇ dark chocolate is used ı ; B : ˇ white chocolate is used ı ; Na : ˇ the chocolates are plain ı ; C : ˇ the chocolates are filled with caramel ı ; All results will be given in decimal form. 1 Draw the probability tree associated with this situation. 2 A box is chosen at random from the factory output. De-termine the probabilities of the following events : a ˇ The box contains dark and plain chocolates ı b ˇ The box contains dark or plain chocolates ı 3 The company sets the prices of the boxes as follows : the base price of a box of chocolates is 9 e ; if dark chocolate is used, the price is increased by 4 e ; if white chocolate is used, the price is increased by 2 e ; if the chocolates are filled with caramel, the price of the box increases by 2 e . The random variable X associates each box produced by the factory with its selling price. a Draw a table representing the probability distribution associated with the random variable X . b Determine the expected value of the random variable X . https://chingmath.fr chapExoCorrec/5196 sacados/5196 chapExoCorrec/6631 sacados/6631 chapExoCorrec/4890 sacados/4890
CCMCCTCCP E.7561 A nursery offers three types of trees : acacias, plane trees, and oaks. Each of these trees can be purchased in different sizes : either as a ˇ young sapling ı ( 0.75 meters) , or as an ˇ mature tree ı ( 2 meters) . At the âsapling stage, acacias, plane trees, and oaks are worth 50 e , 65 e and 80 e respectively. If the customer wants to buy the adult form, they must add 15 e . During his end-of-year review, he notes that 40 % of the trees sold are oaks and that acacias and plane trees share the re-maining sales equally. He also notices that regardless of the type of tree, a quarter of sales are always for " adult ı. The random experiment considered consists of randomly drawing an invoice from the fiscal year 2015 . Consider the following events : A : ˇ The tree purchased is an acacia ı P : ˇ The tree purchased is a plane tree ı C : ˇ The tree purchased is an oak tree ı J : ˇ The tree is a young sapling ı 1 a Draw a weighted tree representing this situation b Give the probability of the event C J 2 We consider the random variable X associating the in-voice drawn with its amount. a Draw up the probability distribution table for the ran-dom variable X . b Calculate the expected value of the random variable X . E.4822 A restaurant offers two types of dessert on its menu : an assortment of macarons, chosen by 50 % customers ; a slice of tarte tatin, chosen by 30 % customers. the rest of the customers do not order any dessert. No customer orders more than one dessert. In addition, 80 % customers have coffee, regardless of whether or not they have dessert. A customer at this restaurant is randomly surveyed. We note p the probability associated with this random experiment. We note : M the event : ˇ The customer orders an assortment of macarons ı ; T the event : ˇ The customer takes a slice of tarte tatin ı ; P event : ˇ The customer does not take any dessert ı ; C event : ˇ The customer has a coffee ı and C the opposite event of C . 1 Complete the probability tree below : 2 Determine the probability that a customer chose the mac-aron assortment and had a coffee. 3 An assortment of macarons is sold 6 e , a slice of tarte tatin is sold 7 e , and a coffee is sold 2 e . Each customer orders one dish (and only one) at a single price of 18 e , and does not order more than one dessert or more than one coffee. We denote X the random variable associating each cus-tomer with the price of their bill. a Determine the values taken by the random variable X . b Draw up a table representing the probability distribu-tion of the random variable X . c Determine the expected value of the random variable X . https://chingmath.fr chapExoCorrec/7561 sacados/7561 chapExoCorrec/4822 sacados/4822 CCMCCTCCP
FGMCFGMC RRSpRRSnRRSr ESESESESESESES E.4823 A red fruit producer offers rasp-berries, redcurrants and blueberries for direct sale. The customer can buy either trays of fruit for tasting, or trays of fruit for jam. The grower has noticed that, among his customers, 9 sur 10 purchase a tray of fruit for jam. Regardless of the type of tray purchased, in 50 % des cases the customer chooses blueberry for fruit, 30 % raspberries in the other cases, redcurrant is chosen. Note: C the event : ˇ le customer buys a punnet of fruit at con-fiture ı ; F l the event : ˇ the customer requests raspberries ı ; G the event : ˇ le customer requests groseilles ı ; M l’event : ˇ le customer requests myrtilles ı ; It is assumed that the fruit chosen does not depend on the type of tray purchased and that each customer buys only one tray. 1 Complete the probability tree below : 2 Determine the probability of C F . 3 The producer sets the prices of his trays as follows : The base price of a punnet of fruit for jam is 5 euros and that of a punnet of fruit for eating is 3 euros ; If the selected tray contains raspberries, he adds 1 eu-ros to the price of the tray; If the selected tray contains blueberries, he adds 2 eu-ros to the price of the tray; If the selected punnet contains redcurrants, the base price remains unchanged. We note X the random variable associating each cus-tomer with the price of the punnet purchased. a What are the values taken by the random variable X ? b Draw up a table representing the probability distribu-tion of X . c Determine the expected value of the random variable X . E.4837 A sports shop offers downhill skis, snowboards, and cross-country skis for rent. Its rental equipment consists of 60 % downhill skis, with the remainder divided equally between snowboards and cross-country skis. After each day of rental, the equipment is checked and re-paired if necessary. Regardless of the type of equipment rented, 30 % of the equipment requires repair. Each piece of rented equipment is listed on a form that tracks its status. A form is selected at random. The following events are considered : S p : ˇ The card is for a pair of downhill skis ı ; S n : ˇ The record is for a snowboard ı ; S r : ˇ The record is for a pair of touring skis ı ; R : ˇ The equipment needs repair ı ; R is its opposite event. All results for the first four questions will be rounded to 10 3 . 1 Copy and complete the probability tree below : 2 a Calculate the probability that the card drawn con-cerns a pair of piste skis not in need of repair. b Calculate P S p R : the probability that the card drawn concerns a pair of piste skis or equipment not requiring repair. 3 The cost of renting downhill skis or a snowboard is 20 e , that of a pair of touring skis is 15 e . In the event of repair, an additional cost of 15 e est will be charged. Consider the random variable X which associates the as-sociated billing amount with a plug. a Draw a table representing the probability distribution of the random variable X . b Determine the expectation of the random variable X . 13. Bernoulli test E.7827 Consider an experiment with two possible outcomes : one called ˇ suc-cess ı and denoted S with probabil-ity 0.4 ; the other called ı failure ı and denoted E . We decide to repeat this same ex-periment three times. We obtain the probability tree shown oppo-site. We assume that these repetitions are independent of each other. https://chingmath.fr chapExoCorrec/4823 sacados/4823 FGMCFGMC chapExoCorrec/4837 sacados/4837 RRSpRRSnRRSr chapExoCorrec/7827 sacados/7827 ESESESESESESES
SESESESESESESE SESESESESESESESESESESESESESESE ESESESESESESESESESESESESESESES ESESESESESESESESESESESESESESESESESESESESESESESESESESESESESESES 1 Complete this probability tree? 2 a How many paths have 3 successes? b Give the probability of obtaining three successes at the end of this random experiment. 3 a How many paths have 0 successes? b Give the probability of obtaining no successes at the end of this random experiment. 4 a How many paths have 2 successes? b Give the probability of obtaining exactly two successes at the end of this random experiment? E.4887 Here are the choice trees associated with repeating a Bernoulli test 3 and 4 times respectively: 1 For the threefold repetition of Bernoulli’s test, complete the table below : Number of succès 0 1 2 3 Number of issues 2 a For the fourfold repetition of Bernoulli’s test, com-plete the table below : Number of succès 0 1 2 3 4 Number of issues b Is there a method for obtaining the second table from the first? E.4886 In a game arising from a random exper-iment, only two outcomes are considered : success ( S ) at this game and failure ( E ) . The probability of success is 0.15 . Part A : successive, independent repetition of 4 games Here is the choice tree corresponding to this repetition of ex-periments ; 1 Determine the probability of the event A : ˇ The player won exactly 3 fois ı 2 Determine the probability of the event B : ˇ The player won exactly 2 fois ı Part B: successive and independent repetition of 5 games Here’s the choice tree corresponding to this game: 3 Determine the probability of the event C : ˇ The player won exactly 3 fois ı. https://chingmath.fr chapExoCorrec/4887 sacados/4887 SESESESESESESE SESESESESESESESESESESESESESESE chapExoCorrec/4886 sacados/4886 ESESESESESESESESESESESESESESES ESESESESESESESESESESESESESESESESESESESESESESESESESESESESESESES
PFPFPFPFPFPFPFPFPFPFPFPFPFPFPF SESESESESESESESESESESESESESESE E.389 1 A player flips an unbalanced coin with a probability of 0 ; 63 of landing on heads. What is the probability of landing on tails? We want to examine certain outcomes resulting from four tosses of this coin. We assume that these tosses are indepen-dent of one another. Note: The elementary events P - P - F - P and P - F - P - P are different outcomes of this random experiment, but each of them results in the same number of heads and tails. 2 a How many outcomes correspond to getting 3 heads and 1 tails? b What is the probability of an outcome containing 3 heads and 1 tails? c Use this to determine the probability of getting 3 heads during this experiment. 3 a Which of the following calculations represents the probability of a roll with exactly 2 heads : (1 0 ; 63) 2 ; 0 ; 63 3 × (1 0 ; 63) 0 ; 63 2 × (1 0 ; 63) 2 ; 0 ; 63 × (1 0 ; 63) 3 b Determine the probability of getting 2 heads during this roll. E.4911 1 Consider the choice tree below from the fourfold repeti-tion of a Bernoulli trial: Determine the binomial coefficients below : a 4 2 b 4 3 2 Using the calculator, determine the value of the following binomial coefficients : a 5 3 a 12 5 a 8 6 a 7 2 14. Binomial law E.7830 A player has a balanced cubic die whose faces are numbered from 1 to 6 . On each throw, he wins if he gets 2 , 3 , 4 , 5 or 6 ; he loses if he gets 1 . A game consists of 5 successive, independent throws of the die. Determine the exact probability that the player will lose 3 times during a game, then its value rounded to the tenth. E.7831 Consider a random variable X following the binomial distribution with parameters n =15 and p =0.63 . 1 Using a calculator, determine the following binomial co-efficients : a 15 13 b 15 14 c 15 15 2 Using a calculator, give the value rounded to the nearest 10 4 of the following probabilities : a P X =13 b P X =14 c P X =15 3 Deduce the value, rounded to the nearest 10 4 , of the probability of event X 12 . E.4938 Let X be a random variable following a binomial distribution with parameters n =35 and p =0.34 . Determine the exact value and then the value rounded to 10 5 of each of the following probabilities : a P X =5 b P X =10 c P X =25 E.4926 Consider a random variable X following the binomial distribution with parameters n =15 and p =0.63 . We will give the exact probability of each of the probabilities requested. 1 Determine the following probabilities : a P X =0 b P X =1 c P X =5 2 Give the probability of event X 14 . https://chingmath.fr chapExoCorrec/389 sacados/389 PFPFPFPFPFPFPFPFPFPFPFPFPFPFPF chapExoCorrec/4911 sacados/4911 SESESESESESESESESESESESESESESE chapExoCorrec/7830 sacados/7830 chapExoCorrec/7831 sacados/7831 chapExoCorrec/4938 sacados/4938 chapExoCorrec/4926 sacados/4926
0123450,10,20,30,4 3XV2F2F2FV2V1F1F1FF2V1F1F1FF2V1F1F1FFV2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF 1414143XV342FV34142V341FFV3414142V341FV34141V340FFF E.4928 A random variable X is assumed to fol-low a binomial distribution with parameters n =5 and p =0.6 . 1 Using a calculator, draw up a table representing the law of the variable X with probabilities rounded to the near-est thousandth. 2 Deduce the following probabilities rounded to the hun-dredth : a P X 1 b P X > 1 E.4930 1 Consider the random variable X following a binomial dis-tribution with parameters n =5 and p =0.5 . a Using a calculator and rounding values to 10 4 , draw up a table showing the probability distribution of the random variable X . b Draw the bar chart representing the law of the random variable X . 2 Consider the random variable X following a binomial dis-tribution with parameters n =5 and p =0.37 . a Using the calculator and rounding values to 10 4 , draw up a table showing the probability distribution of the random variable X . b Draw the bar chart representing the law of the random variable X . E.7385 Consider a multiple-choice questionnaire consisting of 3 questions each offering 4 answers, only one of which is correct. We create a random experiment by asking participants to ran-domly answer the questions proposed in the form. This situation is represented by the choice tree below : For each elementary event, we associate the random variable X with the number of correct answers. 1 Give the probability law of the random variable X . For each question in the M.C.Q., the probability of a correct answer is 1 4 and a wrong answer is 3 4 . The choice tree is simplified by the probability tree below : 2 a Using this probability tree, what calculation finds the values of the probabilities : P X =0 ; P X =3 b What method can be one apply to quickly obtain the values of P X =1 and P X =2 ? E.7487 Ten people apply for a job in the company. Their applications are studied independently of each other. We denote by X the random variable giving the number of people recruited among the 10 people. We know 38 % of the applicants have been recruited. 1 Justify that X follows a binomial distribution with pa-rameters n =10 and p =0.38 . 2 Calculate the probability that at least one of the ten peo-ple will be recruited. The exact value and then a value of the result rounded to 10 3 will be given. https://chingmath.fr chapExoCorrec/4928 sacados/4928 chapExoCorrec/4930 sacados/4930 0123450,10,20,30,4 0123450,10,20,30,4 chapExoCorrec/7385 sacados/7385 3XV2F2F2FV2V1F1F1FF2V1F1F1FF2V1F1F1FFV2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF2V1F1F1FV1V0F0F0FF1V0F0F0FF1V0F0F0FFF 1414143XV342FV34142V341FFV3414142V341FV34141V340FFF chapExoCorrec/7487 sacados/7487 Extrait Antilles-Guyanes Juin 2014
Représentation 1 Représentation 2 E.7829 Let X follow a binomial distribution with parameters 15 and 0.35 . C’est-à-dire : XB (15 ; 0.35) Determine the exact value, then the value rounded to the thousandth of the following probabilities : a P X =5 b P X =7 c P X =9 E.7640 By choosing a pupil at random from among those registered for half-board, we know that the probability of the chosen pupil being satisfied with half-board is 0.675 . Each time, a group of 4 students is interviewed. We denote X the random variable equal to the number of stu-dents declaring themselves satisfied with the quality of the meals. As the number of students is sufficiently large, X is considered to follow a binomial distribution. Results will be rounded to the nearest thousandth. 1 Specify the parameters of this binomial distribution. 2 Calculate the probability of the event A : ˇ the four stu-dents are satisfied with the quality of repas ı. 3 Describe in a sentence the event A and calculate its prob-ability. E.4888 Consider an urn containing 6 red balls and 4 blue balls indistinguishable by touch. 1 One ball is drawn at random from this urn. What is the probability of getting a red ball? We decide to draw three balls in succession. Each time, the ball is put back into the urn (the draw is said to be with de-livery) . 2 Consider the Bernoulli scheme resulting from this repeti-tion, where success is associated with the event ˇ having drawn a ball rouge ı a What are the parameters of this Bernoulli scheme? b Construct the tree representing this situation. c How many elementary events realize the event : ˇ having drawn 2 balls rouges ı E.4909 In this exercise, all results will be rounded to the nearest 10 3 . In a city, a survey shows that 87 % of the inhabitants own a cell phone. Three inhabitants are chosen successively, at random and in-dependently. Note X the number of people selected who own a cell phone. 1 What values can the random variable X take? The random variable X is assumed to follow a binomial dis-tribution with parameters 3 and 0.87 : 2 Give, in a table, the probability distribution of the ran-dom variable X ? 3 What is the probability that at least two of his three people own a cell phone? E.4939 Let X be a random variable following a binomial distribution with parameters n =35 and p =0.35 . Using the calculator, determine the following probabilities rounded to the nearest thousandth : a P X 5 b P X 10 c P X 20 E.4937 Of the two representations below and without justification, give the one that represents the law of a random variable X following the binomial law with param-eters n =10 and p =0.3 : E.4929 A random variable X is assumed to follow a binomial distribution with parameters n =8 and p =0.37 . Determine the probability value P 3 X 7 rounded to the nearest hundredth. E.4927 A vaccine is being tested on a popula-tion of 100 individuals. 30 of them react to this vaccine with high fevers. Each test phase is carried out on a group of 5 in-dividuals chosen at random and independently between each test. Let us note X the random variable that associates with each test phase the number of individuals who had a reaction with high fevers. 1 Justify that the random variable X follows a binomial distribution whose parameter values will be specified. 2 Determine the probability that 2 individuals reacted to the vaccine with fever over a test phase. 3 Over a test phase, what is the probability that at least 4 individuals have reacted with fever. https://chingmath.fr chapExoCorrec/7829 sacados/7829 chapExoCorrec/7640 sacados/7640 chapExoCorrec/4888 sacados/4888 chapExoCorrec/4909 sacados/4909 chapExoCorrec/4939 sacados/4939 chapExoCorrec/4937 sacados/4937 Représentation 1 Représentation 2 chapExoCorrec/4929 sacados/4929 chapExoCorrec/4927 sacados/4927