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Math Help - law of iterated variance problem

  1. #1
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    law of iterated variance problem

    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)
    Y=I(1)+I(2)

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

    thanks for your help!
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  2. #2
    MHF Contributor matheagle's Avatar
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    Thanks
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    1) I assume n=N
    2) are we replacing the balls after we select them?
    you need to find the joint distribution of X and Y
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