試題詳解

21. A health study tracked a group of persons for five years. At the beginning of the study,20% were classified as heavy smokers, 30% as light smokers, and 50% as nonsmokers.
 Results of the study showed that light smokers were twice as likely as nonsmokers to die during the five-year study, but only half as likely as heavy smokers.
 A randomly selected participant from the study died during the five-year period.
 Calculate the probability that the participant was a heavy smoker.
(A) 0.20
(B) 0.25
(C) 0.35
(D) 0.42
(E) 0.57