Remember with conditional probability, such as probability of event A given event B is defined as follows: P(B/A) = P(A and B)/P(A) P(A and B) = P(A)P(B) if events A and B are independent, therefore if A and B are independent, P(B/A) = P(B) and P(A/B) = P(A) If A and B are not independent then P(A and B) = P(A/B)P(B)