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?
答案是A. 6 to 1
我算出来是6to 5呢，C105/C104
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答案应该是 C105P55/C104P44
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发表于 2009-1-22 20:55:00
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