曼哈顿的题目。。求大神解答

c87538 · 发表于 2015-8-12 08:57:29

In a room filled with 7 people, 4 people have exactly 1 sibling in the room and 3 people have exactly 2 siblings in the room. If two individuals are selected from the room at random, what is the probability that those two individuals are NOT sibling？

c87538 · 发表于 2015-8-12 09:03:28

自己顶！d=====(￣▽￣*)b

c87538 · 发表于 2015-8-12 09:12:04

没有人嘛

c87538 · 发表于 2015-8-12 09:23:15

继续顶

guoyilin2015 · 发表于 2015-8-12 09:27:55

a1 a2 a3 b1 b2 c1 c2

Cxy是组合符

1 - (C32 + C21 + C21) / C72 = 16/21

c87538 · 发表于 2015-8-12 09:32:21

guoyilin2015 发表于 2015-8-12 09:27
a1 a2 a3 b1 b2 c1 c2

Cxy是组合符

4 people have exactly 1 sibling in the room and 3 people have exactly 2 siblings in the room. 这两句话理解不了。。。能翻一下么

guoyilin2015 · 发表于 2015-8-12 10:04:39

c87538 发表于 2015-8-12 09:32
4 people have exactly 1 sibling in the room and 3 people have exactly 2 siblings in the room. 这 ...

sibling意为兄妹是相互关系

4个人有且只有一个sibling
那么两人一组 c1c2互为sibling b1b2互为sibling

3个人有且只有两个sibling同理
a1a2a3互为sibling

guoyilin2015 · 发表于 2015-8-12 10:06:47

c87538 发表于 2015-8-12 09:32
4 people have exactly 1 sibling in the room and 3 people have exactly 2 siblings in the room. 这 ...

感觉数学刷真题OG和PREP足矣，没必要manhattan

DANIELLLLLL · 发表于 2015-8-12 10:26:27

guoyilin2015 发表于 2015-8-12 10:06
感觉数学刷真题OG和PREP足矣，没必要manhattan

大神！我看了你几次数学解答，相当流弊！你的名字让我想起一位大神GL莫非是本尊降临？

c87538 · 发表于 2015-8-12 10:36:28

guoyilin2015 发表于 2015-8-12 10:06
感觉数学刷真题OG和PREP足矣，没必要manhattan

懂啦。。thank you

曼哈顿的题目。。求大神解答

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