q**********n
发帖数: 262 | 1 一个pool中有10种不同颜色的球，每种都有足够（无限）多个。
现在从pool中取20次，求这20个球cover了所有10种颜色的概率。
有一种颜色的概率好求，不过同时有10种颜色概率怎么求呢？
谢谢 | Q***5
发帖数: 994 | 2 There are totally 10^20 possibilities, you need to find out how many of them
have all 10 colors show up. Let that number be f(10), similarly, let f(k)
be the number of possibilities of exactly k colors show up in 20 draws.
f(10) = 10^20- C(10,9)f(9)- ... C(10,1)f(1)
f(9) = 9^20-C(9,8)f(8) .....
....
You can then solve for f(10).
This is a straightforward approach, but there might be some easier ways. | m********8
发帖数: 123 | 3 确信这个题目对吗？？？
“每种都有足够（无限）多个”就完啦？
假如
case 1： 1万个红球，1000个蓝球，剩余的情况为A
case 2： 5000个红球，6000个篮球，剩余的情况为A
case 1 和 case 2 能算出同样的概率？
难道是“无限”在作怪？？
请确认题目是否正确 |
|
