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标题: GWD 17 - 2 [打印本页]

作者: bobiouou    时间: 2005-12-22 07:45     标题: GWD 17 - 2

I can't find any posts on this question. Hope this is not a re-post.

A researcher plans to identify each participant in a certain medical experiment with a code consisting of either a single letter or a pair of distinct letters written in alphabetic order. What is the least number of letters that can be used if there are 12 participants, and each participant is to receive a different code?

A. 4

B. 5

C. 6

D. 7

E. 8

Ans = B


My answer is A. Maybe I didn't get through the question. My understanding is: can use SINGLE letter or 2 letters. So only need 4 alphabets. 4 letters + 4*3 > 12

Please help!


作者: chinabens    时间: 2005-12-22 21:56

x + C(2,x)>12 ->x at least is 5
作者: nbnhjf    时间: 2005-12-23 07:30

我觉得是这样吧:关键是对in alphabetic order的理解。

原来我是这样想的,可以这样排,如AB、BA、BC

如果选B的话,肯定不能BA这样排。

如果只用两个字母的话,就是C(X,2)>12,X>=4

既用一个字母又用两个字母,就如一楼所算

X大于等于5即可。






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