If a code word is defined to be a sequence of different letters chosen from the 10 letters A, B, C, D, E, F, G, H, I, and J, what is the ratio of the number of 5-letter code words to the number of 4-letter code words?
A. 5 to 4
B. 3 to 2
C. 2 to 1
D. 5 to 1
E. 6 to 1
这到题的解题思路是什么啊 ，怎么不是A啊
作者: wildwind 时间: 2004-6-10 17:39
此题应该用排列就可以了吧: P(5,10)/P(4,10)= 6:1
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