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两袋黑白球:怎样分配让你赢面最大?

100 balls: 50 white and 50 black and two sacks.

专题
Brainteaser / 脑筋急转弯
难度
L2

题目详情

有 100 个球:50 个白球、50 个黑球,以及两只袋子。你可以任意把球分配到两只袋子里。

之后我会选择其中一只袋子(等概率)并从该袋随机摸出一个球:若摸到黑球我赢,摸到白球你赢。

你如何分配,才能使你赢(摸到白球)的概率最大?

Let's play a game with 100 balls: 50 white and 50 black and two sacks. You can arrange the balls within the two sacks in any way you want. I then come into the room and pick a ball from one of the sacks. If I pick a black, I win; a white, you win. How do you arrange the balls such that you have the highest chance of winning?

解析

最优分配是:

  • 袋 1:放 1 个白球;
  • 袋 2:放剩余的 49 白 + 50 黑(共 99 个)。

则赢的概率为

121+124999=74990.7475.\frac{1}{2}\cdot 1+\frac{1}{2}\cdot\frac{49}{99}=\frac{74}{99}\approx 0.7475.

这是经典最优解。