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!
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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