gwd-6-3的答案到底是什么阿?

jessica628

If a committee of 3 people is to be selected from among 5 married couples so that the committee does not include two people who are married to each other, how many such committees are possible?

A.      20

B.      40

C.      50

D.     80

E.      120

答案给的是d,另一个版本是e,可是我怎么看来看去也认为是a.我的思路是从5对中选三对(这三个人肯定来自不同的couple),在这三对中分别选一.,请大家帮我看看.

erfan

本题思路：

先考虑从10人中直接选3人，然后从中减去从5对中挑一，式子如下：

C10,3 - C5,1 X C8,1