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
请问这个选哪个呢?GWD里面选的是E。不解。谢谢!作者: sealg 时间: 2012-2-12 10:09
我觉得选E。
这是个permutation题。
5个字母:10x9x8x7x6
4个字母: 10x9x8x7
比例:6:1
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