Q5: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 4B.3 to 2C.2 to 1D.5 to 1E.6 to 1
这道题是不是C10 5 :C10 4 ?可是答案是E, 困惑,请求各位好心人指教.
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要排序的亚~p10 5/p10 4=6:1
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