这种题目,如何下手? 请教思路, 先谢过!!!

lifenlifenlifen · 发表于 2004-5-13 08:15:00

don't know why all of a sudden, i can't type Chinese anymore. Sorry i have to use English.

Here is the question:

6 letters, 2 of them are the same and must be separated by at least one letter. Ask how many ways of combination?

Thanks you very much. I appreciate your help!!!!!

dajiqi · 发表于 2004-5-13 10:17:00

xiaoxin...

mariezhu · 发表于 2004-5-13 11:38:00

P(4,4)*C(5,2)

horsefish · 发表于 2004-5-13 11:47:00

P(6,6)-P(5,5)

juniya · 发表于 2004-5-13 12:10:00

should be p66 / 2 - p55

harvardstudent · 发表于 2004-5-13 13:46:00

agree with juniya

tianwan · 发表于 2004-5-13 14:11:00

juniya，NN。

mariezhu · 发表于 2004-5-13 16:57:00

两种做法的答案是一样的

一种是先排列,减去字母相邻的情况

另一种是将4个字母先排列,然后把这2个字母插进去

所属分类: GMAT考试