[求助]GWD31套-1-25

regine_lin

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

我想我是没读懂题目要求，为什么我只觉得有两种呢？答案是5种。

请大牛们指点 谢谢！！~

zmc_tim119

是有5种..

我们假设6人身高分别为1,2,3,4,5,6

那有5种方法符合要求:

456    356    256    246   356

123    124    134    135   125 

 

 

jeffy1010

顶一下楼上的

这题开始时我以为用算的，汗，后来发现还是得一点点排出来啊

zmc_tim119

其实..概率题 我基本都是排的..哈哈

regine_lin

呵呵 谢谢2楼的指导 我开始一直钻牛角尖 以为只有

456   246

123   135 呢~~