Question

Consider the sample space S = {1, 2, 3, . . ., 10}. Let A = all odd numbers in S. Let B = all multiples of 5 in S. Compute P(B | A). Enter your answer as a fraction using the "/" and do not include spaces in your answer.

Answer 1

A={1,3,5,7,9}
B={5,10}
A∩B={5}
Assuming random sampling,
P(B)=|B|/|S|=2/10=1/5
P(A)=|A|/|S|=5/10=1/2
P(A∩B)=1/10

Finally,
P(B|A)=P(B∩A)/P(A) (by definition)

I'll let you take it from here.

Answer 2

actually it's 2/10