题目

SAT数学题,有关概率
A, B, C, D ,E , F, G
a list consists of all possible three-letter arrangements formed by using the letters above such that the first letter is D and one of the remaining letters is A. if no letter is used more than once in an arrangement in the list and one three-letter arrangement is randomly selected from the list, what is the probability that the arrangement selected will be DCA?

提问时间：2021-01-16

答案

第一个确定是D
然后后面的定有一个是A
就剩C
那么就是(D)+(A)+(B/C/E/F/G)
或者 (D)+(C)+(B/A/E/F/G)...
那就很清楚是1/10的概率...
= =!...
唉