試題詳解

92. A mattress store sells only king, queen and twin-size mattresses. Sales records at the store indicate that the number of queen-size mattresses sold is one-fourth the number of king and twin-size mattresses combined. Records also indicate that three times as many king-size mattresses are sold as twin-size mattresses.
Calculate the probability that the next mattress sold is either king or queen-size.
(A) 0.12
(B) 0.15
(C) 0.80
(D) 0.85
(E) 0.95