请教大牛一道排列组合题！

equalgirl · 发表于 2013-4-30 16:02:31

Q33:

A photographer will arrange 6 people of 6different heights for photograph by placing them in two rows of three so thateach person in the first row is standing in front of someone in the secondrow. The heights of the people withineach row must increase from left to right, and each person in the second rowmust be taller than the person standing in front of him or her. How many such arrangements of the 6 peopleare possible?

A. 5

B. 6

C. 9

D. 24

E. 36

Answer: A?

equalgirl · 发表于 2013-4-30 17:08:46

equalgirl · 发表于 2013-4-30 18:13:36

RobinCamel · 发表于 2013-4-30 19:30:45

同意楼主的答案，我是这样分析的：
1. 最高的跟最矮的其实位置已经固定了
2. 剩下的4个人要分成两排，排内的位置其实也固定了，那么就是4*3/2 = 6
3. 排除掉一种情况：第一排不能把第4跟第5高的都选了，所以结果是5

请教大牛一道排列组合题！

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