使用Combination是否会导致重复计数？

问题如下：

A manager will select 20 bonds out of his universe of 100 bonds to construct a portfolio. Which formula provides the number of possible portfolios?

选项：

A.

Permutation formula

B.

Multinomial formula

C.

Combination formula

解释：

C is correct.

The combination formula provides the number of ways that r objects can be chosen from a total of n objects, when the order in which the r objects are listed does not matter. The order of the bonds within the portfolio does not matter.

本题只是抽出来了20只，没有强调还需要再排序，那么直接选择组合。