How many different 6-letter sequences are there that consist of
A. 6
B. 60
C. 120
D. 360
E. 720
没看懂题意, 请各位指点
答案是b?
先6个数字全排列,P66,然后除以重复的可能P33(三个C是无差别的)和P22(三个B是无差别的),即:
P66/(P33*P22)=720/(6*2)=60
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