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law of iterated variance problem


New member
Feb 26, 2011
There are 2*N balls inside a jug. N of them black and n are white.
call I(1)=0 if the first ball we took out is black
I(1)=1 if the first ball we took out is white
same for I(2),
I(2)=1 if the second ball we took out is white
I(2)=0 if the second ball taken out is black

now X=I(1)

compute E(Var(Y|X))
E stands for expectancy
Var stands for Variance

thanks for your help!