gwd1-25

sophialj

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

答案是a,怎么算得阿，谢谢了！

faster727

我做这道题是是按高矮顺序把这6个人编号：1，2，3，4，5，6；然后穷举。举出5种。应该还有更好的方法吧

sophialj

这种方法不太保险，数字多了容易错，期待更好的方法，不过谢谢faster727

cdcdcdd

画个图吧，两行三列，6在右上，1在左下，5在中上或右下