Let A and B be events defined on a sample space S. If the probability that at least one of them occurs is 0.3 and the probability that A occurs but B does not is 0.1, what is P(B)? Solution P(AUB)=0.3 P(AUB\')=0.1 or P(B\')-P(A\'B\')=0.1 P(AUB)=P(A)+P(B)-P(AB) P(A\'B\')=1-P(AUB) =0.7 or 1-P(B)=0.8 or P(B)=0.2.