Sunday, 17 January 2016

strategy - How to survive, with statistics


You are kidnapped and your offender plays a game with you. In front of you are 2 boxes, containing a total of 50 white balls and 50 black balls. The kidnapper will pull out a ball from one of the two boxes, at random. If the ball is white you survive, if not, you are shot.





  • Every ball must be in one of the boxes.

  • No balls can be left out.

  • Each box must have at least one ball.



Box 1: 25 black balls and 25 white balls Box 2: 25 black balls and 25 white balls.


In this example the chance to live is obviously $50 \% $. How can you distribute the balls so as to increase that chance?



Answer



Box 1: 50 black balls, 49 white balls Box 2: 0 black balls, 1 white ball.
In this example the chance to live is obviously $50\%+50\%*49/99 \approx 75\%$. There is no way to increase that chance.



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