31套题的答案详解讨论贴有么？

shityou

如题。另外请教一道题目：

In a corporation, 50 percent of the male employees and 40 percent of the female employees are at least 35 years old.  If 42 percent of all the employees are at least 35 years old, what fraction of the employees in the corporation are females?

 

A.      3/5

B.      2/3

C.      3/4

D.     4/5

E.      5/6