问题如下：
Owners in residential compounds want to select 3 of 5 residents to be the new members of the owners committee. How many possible outcomes may occur?
选项：
A.10
B.20
C.15
解释：
A is correct. According to the combination formula
In this case, n = 5 and r = 3, we can calculate that 5!/[(5 – 3)!3!] = 10.
老师，该题为何是5C3，我的理解应该是抽出3个、4个、5个的概率相加，所以还需要总人数。。。难道题目理解有误，应该是从居民中抽取3-5人加入居委会，问可能性有多少种吧？
