Outside the high school program / Bernoulli and binomial distribution 23 exercises (including 20 corrected)

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1. Confidence and fluctuation intervals E.5435 Consider a random variable fol-lowing a binomial distribution with parameters 9 and 0.3 : XB 9 ; 0.3 The table below provides information on the probability dis-tribution of the random variable X : k 0 1 2 3 4 5 6 7 8 9 P ( X k ) 0.04 0.196 0.463 0.73 0.901 0.975 0.996 1.0 1.0 1.0 Justify that the random variable X has at least 95 % chance of taking its values in the interval 0 ; 5 . E.5434 Consider a random variable follow-ing a binomial distribution with parameters 9 and 0.5 : XB 9 ; 0.5 The table below provides information on the probability dis-tribution of the random variable X : k 0 1 2 3 4 5 6 7 8 9 P ( X k ) 0.002 0.02 0.09 0.254 0.5 0.746 0.91 0.98 0.998 1.0 1 For which values of k do we have : P X k > 0.025 ? 2 For which values of k do we have : P X k 0.975 ? 3 Justify that the random variable X has at least 95 % chance of taking its values in the interval 2 ; 7 . E.5436 Consider a random variable X follow-ing a binomial distribution with parameters 30 and 0.32 : XB 30 ; 0.32 k 0 1 2 3 4 5 6 7 8 P ( X k ) 0 0 0.001 0.005 0.018 0 ; 049 0.11 0.208 0.341 k 9 10 11 12 13 14 15 16 17 P ( X k ) 0.494 0.645 0.774 0 ; 871 0.934 0.97 0.988 0.995 0.999 k 18 19 20 21 22 23 24 25 26 27 28 29 30 P ( X k ) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Determine the smallest integers a and b such that : P X a ) > 0.025 ; P X b 0.975 2 Justify that : P a X b 0.95 3 Noting F = X 30 the random variable representing the ran-dom frequency of success. Justify that : P a 30 F b 30 0.95 E.5445 Consider the random variable X follow-ing the binomial distribution with parameters 20 and 0.34 : XB 20 ; 0.34 The questions will be answered without justification and us-ing the calculator. 1 Determine the two smallest integers a and b verifying the inequalities: P ( X a ) > 0.025 ; P ( X b ) 0.975 2 Determine the fluctuation interval J at the threshold of 95 % . E.5438 Consider a random variable X following a binomial distribution with parameters 100 and 0.81 . k 71 72 73 74 75 76 77 78 79 P ( X k ) 0.010 0.018 0.032 0.053 0.084 0.127 0.185 0.257 0.343 k 80 81 82 83 84 85 86 87 88 P ( X k ) 0.439 0.540 0.640 0.733 0.813 0.877 0.924 0.957 0.977 Determine the fluctuation interval at 95 % . E.5490 Consider a random variable X follow-ing a binomial distribution with parameters 100 and 0.35 ( XB (100 ; 0.35) ) . The following questions are to be answered using a calculator, and the results should be given to three decimal places where necessary : 1 Determine the value of the following probabilities : a P X =43 b P X 38 c P X 31 2 a Determine the value of the smallest integers a and b that satisfy the following two conditions : P X a > 0.025 ; P X b 0.975 b Give the fluctuation interval at 95 % of the frequency associated with the random variable X . E.5446 One company claims that 80 % of its customers are satisfied with its products. 1 A consumer association wishes to verify this claim and commissions a study of 50 customers of this company. a Determine the fluctuation interval at the threshold of 95 % . b The study obtains a satisfaction rate of 71 % . Accord-ing to this study, what can we say about the company’s affirmation at the threshold of 5 % ? 2 The association renews its study, this time focusing on 100 customers. This new study still obtains a satisfaction rate of 71 % . What can we say about the company’s assertion at the threshold of 5 % . https://chingmath.fr chapExoCorrec/5435 sacados/5435 chapExoCorrec/5434 sacados/5434 chapExoCorrec/5436 sacados/5436 chapExoCorrec/5445 sacados/5445 chapExoCorrec/5438 sacados/5438 chapExoCorrec/5490 sacados/5490 chapExoCorrec/5446 sacados/5446
E.5449 Consider a game using two urns contain-ing balls of indistinguishable red and blue colors. The draws in the two urns are assumed to be independent of each other. Here is the composition of each of the urns : The A est urn composed of three red balls and two blue balls ; The B urn is made up of 12 red balls and 28 boules blue balls. Each participant must remove one ball from the A urn, then one ball from the B urn. 1 a Construire a probability tree representing this game. b Show that the probability of getting at least one red ball has value 18 25 2 We repeat 20 times this game independently. Consider the random variable X which counts the number of games in which at least one red ball has been drawn. a What is the probability law followed by the random variable X ? b Determine the probability of P X 18 . Then, give the value rounded to the nearest thousandth of this probability. 3 a Determine the fluctuation interval at 95 % of the bi-nomial distribution of a random variable Y following a binomial distribution with parameters 100 and 18 25 . b A statistical study was conducted on the repetition 100 times of this game. The frequency of occurrence of the event ˇ at least one red ball was obtained ı was 0.55 . Should this study be rejected with a risk of 5 % ? E.7851 A farm sorts its tomatoes according to size (cali-bre) . It informs its suppliers that 40 % of its toma-toes are of a calibre greater than or equal to 6 (a diameter greater than 47 mm ) . Visiting the farm, a supplier takes 30 tomatoes and observes that, among them, 10 tomatoes are of a size greater than or equal to 6 . Opposite is the cumulative distribution function of a binomial random variable with parameters 30 and 0.4 . The following results can be extracted from it: P X 10 0.2915 ; P X 20 0.9991 1 a Determine the value of the smallest integer a that satisfies the condition : P X a > 0.025 b Determine the value of the smallest integer b that sat-isfies the condition : P X b 0.975 c Deduce the fluctuation interval at the threshold of 95 % of the observed frequency for the random variable X . (The limits will be rounded to 10 3 ) 2 What can be said about the supplier’s observation? 2. Old annuals (pre-2011 program) E.3127 A player has an urn containing 3 red balls, 4 white balls and n green balls ( 0 n 10 ) . The balls are indistinguishable to the touch. 1 The player randomly draws a ball from the urn. Calcu-late the probability of each of the following events : a R : ˇ The ball drawn is rouge ı ; b B : ˇ the ball drawn is blanche ı ; c V : ˇ the ball drawn is verte ı. 2 The player decides to play a game. This takes place as shown below. The player draws a ball from the urn : If it’s red, he wins 16 F ; If it’s white, he loses 12 F ; If it’s green, he puts the ball back in the urn, then draws a ball from the urn ; If this ball is red, he wins 8 F ; If this ball is white, he loses 2 F ; If this ball is green, he neither loses nor gains any-thing. The draws are equiprobable and two successive draws are independent. At the beginning of the game, the player owns 12 F . Let X be the random variable that takes as its value the sum the player owns at the end of the game (one draw or two draws as the case may be) . a Determine the values taken by X . b Determine the probability distribution of X . c Show that the mathematical expectation of X has the value : E ( X )=12+16 · n ( n +7) 2 . 3 Consider the function f defined on the interval 0 ; 10 by f ( x )= x ( x +7) 2 . Study the variations of f . 4 Deduce the value of n for which the mathematical expec-tation X is maximum. Calculate this maximum value (the result will be given as an irreducible fraction) . 3. Truncated geometric law https://chingmath.fr chapExoCorrec/5449 sacados/5449 chapExoCorrec/7851 sacados/7851 chapExoCorrec/3127 sacados/3127 Sportifs de haut-niveau Octobre 1998 4 points
E.7422 Consider the following random experi-ment : throw a die 5 times successively (and independently) and note the throw number where the face 6 first appeared. If the 6 face has not appeared in any of these 5 throws then 0 is noted. 1 Construct the probability tree associated with this ran- dom experiment. 2 Consider the random variable that associates the number denoted with each trial of the random experiment. Determine the probability distribution of the random variable X . 4. Binomial law: fluctuation interval E.4910 Results will be 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 taken suc-cessively, at random and independently of each other. The random variable X 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? The exact value and the value rounded to the nearest thousandth will be given. 3 An engineer is testing the production line. After several batch tests of 10 watches, he obtains 81 % of batches with at least 1 defective watches. What can we say about the state of the production line? E.7858 Consider a random variable follow-ing a binomial distribution with parameters 9 and 0.3 : XB 9 ; 0.3 The table below gives information on the probability distri-bution of the random variable X : k 0 1 2 3 4 5 6 7 8 9 P ( X k ) 0 ; 04 0.196 0.463 0.73 0.901 0.975 0.996 1.0 1.0 1.0 Justify that the random variable X has at least a 95 % chance of taking its values in the interval 0 ; 5 . E.7859 Consider a random variable follow-ing a binomial distribution with parameters 9 and 0.5 : XB 9 ; 0.5 The two tables below give information about the probability distribution of the random variable X : k 0 1 2 3 4 5 6 7 8 9 P ( X k ) 0 ; 002 0.02 0.09 0.254 0.5 0.746 0.91 0.98 0.998 1.0 1 For what values of k do we have : P X k > 0.025 ? 2 For what values of k do we have : P X k 0.975 ? 3 Justify that the random variable X at least 95 % chance of taking its values in the interval 2 ; 7 . E.7857 A farm grades its tomatoes according to their size (calibre) . It informs its suppliers that 40 % of its tomatoes are of a calibre greater than or equal to 6 (a diameter greater than 47 mm ) . Visiting the farm, a supplier takes 30 tomatoes and observes that, among them, 10 tomatoes are of a size greater than or equal to 6 . Opposite is the cumulative distribution function of a binomial random variable with parameters 30 and 0.4 . The following results can be extracted from it: P X 10 0.2915 ; P X 20 0.9991 1 a Determine the value of the smallest integer a that satisfies the condition : P X a > 0.025 b Determine the value of the smallest integer b that sat-isfies the condition : P X b 0.975 c Deduce the fluctuation interval at the threshold of 95 % of the observed frequency for the random variable X . (The limits will be rounded to 10 3 ) 2 What can be said about the supplier’s observation? https://chingmath.fr chapExoCorrec/7422 sacados/7422 chapExoCorrec/4910 sacados/4910 chapExoCorrec/7858 sacados/7858 chapExoCorrec/7859 sacados/7859 chapExoCorrec/7857 sacados/7857
E.141 At a funfair, a lottery is held every hour. Each time, thirty tickets are sold, of which ten are win-ners (it is assumed that all tickets have the same probability of being bought.) . For each result, give the exact value and then the approximate value rounded to the thousandth. 1 Luke buys a ticket. What is the probability that this ticket is a winner? 2 Mark enters three consecutive lotteries for which he takes a ticket each time (the lotteries are assumed to be inde-pendent) . What is the probability that Marc has at least one winning ticket? 3 Peter takes part in a lottery, buying three tickets simul-taneously. a What is the probability that Peter does not have a winning ticket? b What is the probability that Peter has at least one winning ticket? 4 Who is more likely to have at least one winning ticket, Peter or Mark? 5 The advert announces ˇ Every third ticket is a winner! Buy three tickets! ı. This text suggests that, by buying three tickets, you are sure to win. What can we say about this property? E.7861 Consider a game using two urns contain-ing red and blue balls that are indistinguishable to the touch. Assume that the draws from the two urns are independent of each other. Here is the composition of each urn : Urn A contains three red balls and two blue balls ; Urn B contains 12 red balls and 28 blue balls. Each participant must draw one ball from urn A , then one ball from urn B . 1 a Construct a probability tree representing this game. b Show that the probability of obtaining at least one red ball is 18 25 2 This game is repeated 20 times independently. We have the random variable X , which counts the number of games in which at least one red ball was drawn. a What is the probability distribution followed by the random variable X ? b Determine the probability of P X 18 . Then give the value of this probability rounded to the nearest thou-sandth. 3 a Determine the fluctuation interval at 95 % of the bi-nomial distribution of a random variable Y following a binomial distribution with parameters 100 and 18 25 . b A statistical study was conducted on the repetition of this game 100 times. The frequency of occurrence of the event ˇ at least one red ball was obtained ı ı was 0.55 . Should this study be rejected with a risk of 5 % ? 5. Unclassified financial years E.7114 Approximate results should be rounded to the thousandth. A company mass-produces USB flash drives for the computer industry. A random sample of 100 keys is taken from the day’s pro-duction for checking. The production is large enough for this sampling to be considered a random draw of 100 keys. The probability that a key USB taken at random from one day’s production is defective is 0.015 . Consider the random variable X which, to any sample thus defined, associates the number of defective keys in that sam-ple. 1 Justify that the random variable X follows a binomial distribution, the parameters of which we will determine. 2 Calculate the probabilities p X =0 and p X =1 . 3 Calculate the probability that, in such a sample, at most two keys are defective. E.124 To get to the bus stop at 7 h 30 , which takes her to school, Valerie has a choice of three routes : A , B , or C . The probability that she will choose route A is 1 2 , and the probability that she will choose route B is 1 3 . The probability that she misses the bus that passes at 7 h 30 , knowing that she has chosen route A , is 3 10 , and the probabil-ity that she misses the bus that passes at 7 h 30 , knowing that she has chosen route B is 2 5 , the probability that she misses the bus that passes at 7 h 30 , knowing that she has chosen route C , is 1 2 . 1 In this section, we will give the results in the form of irreducible fractions. a Calculate the probability that Valerie chooses route C . b Construct a probability tree showing the various pos-sibilities. Report the probabilities given in the state-ment. c Calculate the probability that Valerie takes the bus that passes at 7 h 30 and that she has chosen route B . d Show that the probability that Valerie takes the bus that passes at 7 h 30 is 19 30 . e Knowing that Valerie took the bus that passes at 7 h 30 , calculate the probability that she chose route C https://chingmath.fr sacados/141 France - Juin 2001 - 4 points chapExoCorrec/7861 sacados/7861 chapExoCorrec/7114 sacados/7114 chapExoCorrec/124 sacados/124
2 In this section, results will be rounded to the nearest 10 3 . Valerie tries to take the bus that leaves at 7 h 30 four days a week under the same conditions. We assume that for Valerie, catching or missing the bus that passes at 7 h 30 on a given day of the week is indepen-dent of catching or missing the bus that passes at 7 h 30 on another day of the week. a Calculate the probability that Valerie will take the bus that passes at 7 h 30 four times during the week. b Calculate the probability that she will take the bus that passes at 7 h 30 exactly twice during the week. Reminder : the probability of E given F is given by: P F ( E ) = P ( E F ) P ( F ) E.132 The results of a survey of a popu-lation of which 52% of the people are women and 48% men, show that 80% of women and 70% of men play the Lotto at least once a month. 1 One individual from this population is chosen at random. All choices are equiprobable. Note: H : the event ˇ The chosen individual is a man. ı H the opposite event of H , i.e. ˇ The chosen individual is a woman. ı L the event ˇ The individual plays the Lotto at least once a month. ı L the opposite event of L , i.e. ˇ The individual plays the Lotto less than once a month. ı. P H ( L ) the conditional probability of the event L with respect to the event H . A probability tree can be represented. a Calculate the probability of the event H L and then that of the event H L . b Show that the probability of L is equal to 0.752. c Determine P L ( H ) , probability that the chosen individ-ual is a man knowing that he plays Lotto at least once a month. Give the result rounded to 10 4 2 This population being sufficiently large, we repeat four times, independently, under identical conditions (or that can be considered as such) , the experiment in the first question ˇ Randomly select an individual from this popu-lation ı. a Determine the probability that one and only one of the four chosen individuals plays Lotto at least once a month, with the others playing less than once a month. Give the result rounded to 10 4 . b Determine the probability that at least one of the four selected individuals plays Lotto at least once a month. Give the result rounded to 10 4 E.128 All results must be given as irre-ducible fractions. We have a checkerboard in which each of the nine squares is marked with one of the three numbers 1, 2, or 3, as shown in the diagram opposite : Three indistinguishable pawns are randomly distributed on the checkerboard (one pawn per square) and we call S the sum of the three numbers marked on the three squares occu-pied by the pawns. All distributions are equally probable. 1 Write Pascal’s triangle up to the tenth row and deduce 9 3 2 Consider the following events E , F , and G : E : ˇ The sum S is equal to 3 ı ; F : ˇ The sum S is equal to 9 ı ; G : ˇ The sum S is equal to 6 ı a Determine the probabilities P ( E ) and P ( F ) of events E and F . b Show that the probability of event G is equal to 1 3 . 3 Let A be the event ˇ The sum is divisible by 3 ı and B the event ˇ The three pawns are aligned in a column, row, or diagonal ı. a Determine the probability P ( A ) and P ( B ) events A and B . b Calculate the probability P A ( B ) of event B given that event A has occurred. c Are events A and B independent? https://chingmath.fr sacados/132 Japon - Juin 2002 - 7 points - obligatoire sacados/128 Antilles - 2003 - au choix - 6 points
vert.........rougeouorange...rougeouorange...vert......... E.142 To hire staff, a company organizes selection tests. Among the candidates who take the tests, there are 60 % men. A statistical study shows that the company hires 70 % of the male candidates and 80 % of the female candidates. Reminder : The conditional probability of A given B is : P B ( A ) = P ( A B ) P ( B ) Part A At the end of the tests, one person is randomly selected from among all the candidates and interviewed. We note : H the event ˇ the person is a man ı. F the event ˇ the person is a woman ı. E the event ˇ the person is hired ı. E the complementary event (or opposite) of E . 1 a What is the probability P ( F ) that the person inter-viewed is a woman? b What is the probability that the person interviewed is not employed, given that she is a woman? 2 Construct a probability tree illustrating this situation. 3 Calculate the probability P ( E F ) that the respondent is a woman and is not employed. 4 Show that : P ( E )=0 ; 26 Part B In this part, the results will be rounded to the nearest thou-sandth. At the end of the tests, four people are interviewed at random. We will consider that these four choices are independent in pairs. 1 What is the probability that none of the four people will be hired? 2 What is the probability that at least one of the four peo-ple will not be hired? 3 What is the probability that exactly two people will be hired? E.3726 Amélie has to cross the main street of a village, which is lined with two traffic lights. To n 1 ; 2 , we note E n the event ˇ Amélie is stopped by the n e red light or orange ı and E n the opposite event. The orange light is considered a red light. Let p n be the probability of E n and q n that of E n . The probability of the first traffic light being red or amber is 1 8 . It is assumed that the following two conditions are met : The probability of the second traffic light being red or amber, if the first traffic light is red, is 1 20 . The probability that the second traffic light is red or or-ange, if the first light is green, is equal to 9 20 . We’re interested, first of all, in the first traffic lights. 1 Copy and complete the weighted tree below. 2 Note X the random variable equal to the number of green lights among these two traffic lights. Determine the prob-ability distribution of X . https://chingmath.fr chapExoCorrec/142 sacados/142 Liban - Juin 2005 - 7 points chapExoCorrec/3726 sacados/3726 vert.........rougeouorange...rougeouorange...vert.........