数学………………

吊坠 · 发表于 2011-8-9 11:14:33

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

5
6
9
24
36

Tobelogical · 发表于 2011-8-9 11:42:15

我的思路是6个人两两组合，然后3队排列。
觉得应该是36，但是我，我算不出22组合有几种可能，NN指导一下

tinycotton · 发表于 2011-8-12 17:19:56

设六个人分别为123456，按身高排。1只能在前排第一个，6只能在后排第三个。这两个固定之后，
讨论前排中能放的人，只有2和3两种情况，依次再分别列举。
答案五种为
123（456）；124（356）；125（346）；
134（256）；135（246）

吊坠 · 发表于 2011-8-13 17:49:10

谢谢呀~~~

数学………………

所属分类: GMAT考试

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