Can I solve by the following: Suppose that a member of the US Senate is randomly selected. What is the probability that the senator is up for reelection in November 2014, knowing that this senator is a Republican? Event A: A senator is up for reelection in November 2014 Event B: A senator is a Republican Conditional probability in this case is the probability of being up for reelection in November 2014 and that the senator is a Republican, which is calculated as: 13/37 = 0.3513