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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
:
X∼B
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
:
X∼B
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?
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sacados/132
Japon - Juin 2002 - 7 points - obligatoire
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Antilles - 2003 - au choix - 6 points
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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
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