涛涛版GWD1-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可我怎么数来数去只有4种可能呢.以前好象看到过讨论当时也明白的.可是找不到了,在家再帮我分析一下吧

这道题,我是用笨办法,假设170,172,174,176,178,180这六个高度.170,180分别为第一排最左和第二排最右.然后一种一种可能数出来的.

问有没有思路更清楚的解法?

也是用苯办法想的

用123456代替

我也是用123456这样穷举得，有没有高手会算出来？

万一考试的时候是10个20个人怎么办

123     124  125    134    135

456     345   346    256    246