Let A and B be events defined on a sample space S. Suppose that P(A) = 0.4, P(B) = 0.5, and the probability of both occurring is 0.1. What is the probability that either A or B (but not both) occur? Solution P(A) = 0.4 P(B) = 0.5 P(A and B) = 0.1 P(A or B) = P(A) + P(B) - P(A and B) = 0.4 + 0.5 - 0.1 = 0.8 P(either A or B not both) = P(A or B) - P(A and B) = 0.8 - 0.1 = 0.7.