Friday, 21 November 2014

paradoxes - How do you explain this probability paradox?

Imagine there are two bags of money, and you are allowed to choose one. The probability that one of them contains 10n1 dollars and the other contains 10n dollars is 1/2n, n{1,2,3...}.



That is to say, there is 1/2 probability that one of the two bags contains $1 and the other contains $10; 1/4 probability that one of the two bags contains $10 and the other contains $100 , etc.



What's interesting is that, no matter which one you choose, you'll find that the other one is better. For example, if you open one bag, and find there are $10 in there, then the probability of the other bag contains $1 is 2/3 and the probability of the other bag contains $100 is 1/3, and the expectation of that is $34, which is better than $10.



If the other one is definitely better regardless of how much you'll find in whichever one you choose, why isn't choosing the other one in the first place a better choice?

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