填空题 .Let A, B, C, and D be events for which
    P(A or B)=0.6, P(A)=0.2, P(C or D)=0.6, and P(C)=0.5.
    The events A and B are mutually exclusive, and the events C and D are independent.

填空题 24.  Find P(B).

填空题 25.  Find P(D).