The probability that neither occur is the complement of the event that A or B occurs. So we will first calculate P(A or B) P(A or B) = P(A) + P(B) - P(A and B) But since they are mutually exclusive, P(A and B) = 0 P(A or B) = P(A) + P(B) - P(A and B) P(A or B) = P(A) + P(B) - 0 P(A or B) = P(A) + P(B) P(A or B) = 0.21 + 0.05 P(A or B) = 0.26 The complement of the event (A or B) has probability 1 - 0.26 = 0.74 Edwin