GWD-TN1 Q25

5cheng

Q25:

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?



A.5

B.6

C.9

D.24

E.36
求翻译~求解释~

cdcharlie

6个不同身高的人被排成两排照相，一排3人。两排应该是平行的站着，一一对应。每排人的身高从左到右增高。第二排的每个人要比第一排站他前面的高。 问有多少种排法。

zhlee

硬数， 选A

5cheng

我想明白了，老公教会我的~~
可以这样做
  A  B   C
  D   E   F
如上图，a和f是固定的，因为要保证题目中的情况，所以a是最低的，f是最高的
之后的bc位置可以从剩下四个人里面选2个，但是要排除 倒数第二高和第三高 的情况，
式子就是C42-1=5

小羽羽

懂了，不过考试时硬数，忙中易出错