一道关于排列组合的数学题求解答！

方方的地球 · 发表于 2015-2-8 15:15:40

题目如下：
The University of Maryland, University of Vermont, and Emory University have each 4 soccer
players. If a team of 9 is to be formed with an equal number of players from each university, how
many number of ways can the selections be done?
(A) 3
(B) 4
(C) 12
(D) 16
(E) 25

答案选C，书上解释是这样的：
Selecting 3 of 4 players can be done in 4C3 = 4 ways.
The selection from the 3 universities can be done in 3*4 = 12 ways.

我不懂的是为什么这题是把三个学校的选择相加而不是相乘。。因为我觉得是每个学校选出人之后再和别的学校选的人再形成搭配，所以不应该用乘法吗这边？。。

[你问我答] 一道关于排列组合的数学题求解答！

所属分类: GRE考试

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