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        riddles >> putnam exam (pure math) >> Probability... Surprising Answer.
        
(Message started by: Johan_Gunardi on May 20^th, 2007, 9:11pm)

Title: Probability... Surprising Answer.
Post by Johan_Gunardi on May 20^th, 2007, 9:11pm

http://www.qbyte.org/puzzles/p018s.html

I am poor in English. I don't really understand why the answer is 1/2. Can anybody explain it to me?

Title: Re: Probability... Surprising Answer.
Post by towr on May 20^th, 2007, 11:20pm

The problem is symmetric: you keep the same problem when you switch heads and tails in the problem statement.
So the probability of having more heads must be the same as the probability of having more tails. Seeing as those are the only two options, and total probability must add to 1, both must be 1/2.