CONDITIONAL PROBABILITY
(Dependent Events)
conditional probability:
computing the probability of an event
GIVEN that another event has already
occurred
EXAMPLE 1
a)
In the toss of 2 coins, determine the
probability of getting 2 tails.
b)
If the additional information was given
that one coin is a tail, determine the
probability of getting 2 tails.
NOTATION for CONDITIONAL PROBABILITY
P(A/B) “the probability of A given that B has occurred”
METHODS for Computing CONDITIONAL PROBABILITY
1.
Restrict the sample space.
2.
Use the formula:
P(A/B) 
P(A  B)
P(B)
EXAMPLE 2
a)
P(King)
Draw one card from a standard deck. Determine:
b)
P(King/face card)
EXAMPLE 3
Determine the probability of rolling a sum of six
given that doubles are rolled on two dice.
EXAMPLE 4
A weather pattern found that there is an 8%
chance of snow in March. There is a 2% chance
that there will be a snow day at OLMC. Determine
the probability that there will be a snow day at
Carmel given that there was a snow storm in
March.