这题有top5的概念，我觉得排序的12345,和21345就不一样了，因该用p
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No.PZ2021062201000009 (选择题)
来源: 原版书
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：
您的回答, 正确答案是: A
A
142,506
B
不正确17,100,720
C
24,300,000
数据统计(全部)
做对次数: 32
做错次数: 9
正确率: 78.05%
数据统计(个人)
做对次数: 0
做错次数: 1
正确率: 0.00%
解析
A is correct. The number of combinations is the number of ways to pick five stocks out of 30 without regard to order：
{}_n{C_r} = \frac{{n!}}{{(n - r)!r!}}
n
Cr
=(n−r)!r!
n!
$${}_{10}{C_4} = \frac{{30!}}{{(30 - 5)!5!}} = \frac{{30 \times 29 \times 28 \times 27 \times 26}}{{5 \times 4 \times 3 \times 2 \times 1}} = 142,506$$
The contestant’s chance of winning is one out of 142,506.
