求助这题怎么做，谢谢．

whx1862 · 发表于 2010-4-20 23:19:52

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
Answer:
答案是Ｄ，我做的是Ａ

tristanwhistle · 发表于 2010-4-20 23:30:20

C53(5在下面，三在上面)*2*2*2

tanjing · 发表于 2010-4-20 23:33:45

5*2*C(4,2)+2*C(5,3)

Avène · 发表于 2010-4-20 23:56:34

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
Answer:
答案是Ｄ，我做的是Ａ

-- by 会员 whx1862 (2010/4/20 23:19:52)

这三人全是男人：C53 （5在下，3在上）
全是女人：C53
在男或女中选1人：C51乘以C42 （因为不能使他老婆或她老公）
在男或女中选2人：C52乘以C31
=80

selfay · 发表于 2010-4-21 00:20:42

之前是按照4楼那样做的，刚突然傻掉了，不是这样做，发现没算对，最后总算搞明白了，因为今晚是这样算的
C(5,3)P(2,2)P(2,2)P(2,2)=80

5对夫妇选3对，每对选一个人，等于3对都各自做全排列

whx1862 · 发表于 2010-4-21 09:17:25

Thank you.

kaoruya · 发表于 2010-4-21 12:31:33

2楼的解法很清晰啊。。
C(10,3)-C(5,1)*C(8,1)=80
C(10,3)代表10人选3个；C(5,1)*C(8,1)代表5对选1对（2个人了）再从剩下8个人里选1个--就是要排除的选法。

求助这题怎么做，谢谢．

所属分类: GMAT考试

正在浏览此版块的会员 ()