試題詳解

22. (5%) A newly married couple decides to continue having children until they have one of each sex. If the probability of a child being a boy is 1/4 and the probability of a child being a girl is 3/4, how many children should this couple expect?
(A)4
(B)17/4
(C)13/3
(D)9/2
(E)16/3