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
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
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