NO.PZ2021062201000009
问题如下：
Gerd Sturm wants to sponsor a contest with a $1 million prize. The winner must pick the stocks that will be the top five performers next year among the 30 stocks in a well-known large-cap stock index. He asks you to estimate the chances that contestants can win the contest.
What are the chances of winning if the contestants must pick the top five stocks without regard to order?
If choosing five stocks randomly, a contestant's chance of winning is one out of：
选项：
A.142,506
B.17,100,720
C.24,300,000
解释：
A is correct. The number of combinations is the number of ways to pick five stocks out of 30 without regard to order：
$${}_{10}{C_4}
= \frac{{30!}}{{(30 - 5)!5!}} = \frac{{30 \times 29 \times 28 \times 27
\times 26}}{{5 \times 4 \times 3 \times 2 \times 1}} = 142,506$$
The contestant’s chance of winning is one out of 142,506.
$${}_{10}{C_4} = \frac{{30!}}{{(30 - 5)!5!}} = \frac{{30 \times 29 \times 28 \times 27 \times 26}}{{5 \times 4 \times 3 \times 2 \times 1}} = 142,506$$
老师您好，答案中这段描述，没有看懂。
运用组合的方式从30个选择5个（即 30C5）已经清楚，后面的解题思路可以烦请老师讲解一下吗。谢谢老师~
