STAT 408
Examples for 01/28/2009
Spring 2009
The
conditional
probability
of
A,
given
B
(the
probability
of
event
A,
computed
on
the
assumption
that
event
B
has happened)
is
P
(
A
∩
B
)
P
(
A
B
)
=
(
assuming
P
(
B
)
≠
0
)
.
P
(
B
)
Similarly, the
conditional
probability
of
B,
given
A
is
P
(
A
∩
B
)
P
(
B
A
)
=
(
assuming
P
(
A
)
≠
0
)
.
P
(
A
)
C
C
'
B
0.10
0.45
0.55
B
'
0.20
0.25
0.45
1.
The probability that a randomly selected
student at Anytown College owns a bicycle
is 0.55, the probability that a student owns
a car is 0.30, and the probability that a
student owns both is 0.10.
P(B) = 0.55,
P(C) = 0.30,
P(B
∩
C) = 0.10.
0.30
0.70
1.00
a)
What is the probability that a student owns a bicycle, given that he/she owns a car
?
P( B
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 Spring '08
 STEPANOV
 Statistics, Conditional Probability, Probability, 25%, 30%

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