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Math Help - Marginal pdf's

  1. #1
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    Marginal pdf's

    plz help to me, actually I cant find out how to got ans.

    the pdf is given as
    f(x, y) = 2, if (x,y) є R
    else 0

    there is marginal pdf's of X and Y

    = 2y

    then

    E(X) = integral 0 to 1, x2(1-x)dx = 1/3

    now can you describe this stepwise

    E(X) = mathemetical expectation

    becoz I cant analyse it
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by yog782004 View Post
    plz help to me, actually I cant find out how to got ans.

    the pdf is given as
    f(x, y) = 2, if (x,y) є R
    else 0

    there is marginal pdf's of X and Y

    = 2y

    then

    E(X) = integral 0 to 1, x2(1-x)dx = 1/3

    now can you describe this stepwise

    E(X) = mathemetical expectation

    becoz I cant analyse it
    If the original of this question was in English please post the exact wording.

    CB
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  3. #3
    MHF Contributor matheagle's Avatar
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    we need to know where f(x,y)=2
    The support cannot be all of R2.
    probably some triangle with x<y or y<x
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  4. #4
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    Intigral

    Hi Captain
    Hi mathengle

    Here I attach one you can find it,
    actually it is example of my book and cant analyse these calculation
    Attached Files Attached Files
    Last edited by yog782004; December 27th 2009 at 11:49 PM. Reason: Its wrong typed
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  5. #5
    MHF Contributor matheagle's Avatar
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    I'm not sure what you want to know.
    The defintion of the mean of X is

    E(X)=\int_{-\infty}^{\infty}xf(x)dx

    You first need to find the density and the support (where it is not zero).
    Then integrate.

    Likewise E(X^2)=\int_{-\infty}^{\infty}x^2f(x)dx
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  6. #6
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    Lightbulb

    thanks mathegle

    I get somethink from your suggetion, actualy I m not sure in intrigral operation and calculation, thats y i hav this confusion.
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