GWD中第13套-3

shelleyzhdai

Q3:

Each participant in a certain study was assigned a sequence of 3 different letters from the set {A, B, C, D, E, F, G, H}. If no sequence was assigned to more than one participant and if 36 of the possible sequences were not assigned, what was the number of participants in the study? (Note, for example, that the sequence A, B, C is different from the sequence C, B, A.)

A. 20

B. 92

C. 300

D. 372

E. 476

题目看不懂。。。

解释下好么？？感激ing

qiancheng

从8个字母中任取3个不同排序，有36种已排掉，问剩下多少种？
P8,3－36＝336－60＝300
选D。

shelleyzhdai

可是我的答案是C ??

paopaodong

300不是C吗？

Rachmaninoff

 Note, for example, that the sequence A, B, C is different from the sequence C, B, A.) 这句话的意思是不是A，B，C可以有6种不同的组合（A，B，C）（A，C，B），（B，C，A），（B，A，C），（C，A，B），（C，B，A）那这样的话答案也不是C 300了，那答案就应该是8X7X6X6-36

smallzhang

总共可以排C(3,8)*C(1,3)*C(1,2)=336

有36种没有用，也就是说 the number of participants in the study=336-36=300