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标题: 请教数学题 [打印本页]

作者: smilingtracys 时间: 2008-9-26 19:57 标题: 请教数学题

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

key is E.

Why?

作者: quejingui77 时间: 2008-9-27 20:37

P^510/p^4 10=6

作者: williamblacks 时间: 2008-9-28 20:22

6：1
10个里选5个的排列是 10×9×8×7×6
10个里选4个的排列是10×9×8×7
比值是6：1

作者: smilingtracys 时间: 2008-9-30 20:27

 多谢！！！

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