Posted by libeed on Thursday, June 16, 2011 at 5:59pm.
a pair of dice is rolled. is the event of rolling a sum of the dice is an odd number. Find the probability that the sum is a five or a ten, given that an odd sum is rolled.

math  Reiny, Thursday, June 16, 2011 at 7:28pm
The notation for conditional probability is P(BA), read as the probability of B given A.
P(BA) = P(A and B)/P(A)
for yours P(A) = P(odd sum is rolled)
P(B) = P(5 or 10)
ways to get 5: (1,4) (2,3) (3,2) (4,1) > 4 ways
ways to get 10: (4,6) (5,5) (6,4)  > 3 ways
P(A) = 18/36 = 1/2
P(A and B) = P((5or10) and odd) = 4/36
P(BA) (4/36)/(1/2) = 2/9