Gwd-19-Q26:谢谢

newcentury

Gwd-19-Q26:

How many different 6-letter sequences are there that consist of 1 A, 2 B’s, and 3 C’s ?

A.   6

B.    60

C.   120

D.   360

E.    720

Answer:b

一点思路都没有 ，恳求大家帮忙，谢谢

daoying

因为有3个重复的C, 2个重复的B，所以用排列公式，

P55/P33*P22= 5!/3!*2!=60