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DanielLC comments on Probability puzzle: Coins in envelopes - Less Wrong Discussion

8 Post author: HonoreDB 02 December 2011 05:58AM

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Comment author: DanielLC 02 December 2011 06:25:59AM *  4 points [-]

I notice solving problem 2 also solves problem 1.

The solution to two:

sum(f(k)) = sum of f(k) for each value of k from 0 to m inclusive

1/2 = sum(k^2/m)/sum(k)-1/m

= (m(m+1)(2m+1)/6)/(m^2(m+1)/2)-1/m

= (2m+1)/3m-1/m

= (2m+1)/3m-3/3m

= (2m-2)/3m

= 1/2

4m-4 = 3m

m = 4

Four envelopes.