If a code word is defined to be a sequenceof different letters chosen from the 10 letters A, B, C, D,E, F, G, H, I, and J, what is theratio of the number of 5-letter code words to the number of 4-letter codewords?
A. 5 to 4
B. 3 to 2
C. 2 to 1
D. 5 to 1
E. 6 to 1
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因为是code,有顺序之分,所以是需要考虑排列的.
所以就是A105:A104=6:1
答案应该是E吧
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