Let A and B be events in a sample space S such that P(A) = 0.6, P(B) = 0.4, and P(A B) = 0.27. Find the probability

Question

P(B|A)

Answer 1

by definition of conditional probability :
P(B|A) = P(B and A)/P(A)
= .27/.6 = .45

Answer 2

What is Baye's Theorem? http://en.wikipedia.org/wiki/Bayes%27_theorem