試題詳解

140. A certain brand of refrigerator has a useful life that is normally distributed with mean 10 years and standard deviation 3 years. The useful lives of these refrigerators are independent.

Calculate the probability that the total useful life of two randomly selected refrigerators will exceed 1.9 times the useful life of a third randomly selected refrigerator.
(A) 0.407
(B) 0.444
(C) 0.556
(D) 0.593
(E) 0.604