题目是这样的
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,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
B3 to 2
C2 to 1
D5 to1
E6 to 1
答案是E
我连题目都不知道在说什么
救救我吧
10个字母里面选5个字母排列的种类,和10选4排列的种类的比值?
p10,5/p10,4=6/1
答案e
明白了
原来是这意思
谢谢
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