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Thread: Expected Value

  1. #1
    Bar0n janvdl's Avatar
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    Expected Value


    Let: X ~ Poisson( $\displaystyle \lambda$ )

    Find: $\displaystyle E[X(X-1)]$
    There is a certain method to go about doing this. I remember the start and finish, but not the intermediate steps.


    $\displaystyle E[X^2 - X]$

    $\displaystyle = E[X^2] - E[X]$

    ... ... ... ...

    $\displaystyle = \lambda + \lambda ^2 - \lambda$

    $\displaystyle = \lambda ^2$
    Or something like it. It had to do with the fact that E[X] in this case = $\displaystyle \lambda$
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  2. #2
    Flow Master
    mr fantastic's Avatar
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    Quote Originally Posted by janvdl View Post
    There is a certain method to go about doing this. I remember the start and finish, but not the intermediate steps.



    Or something like it. It had to do with the fact that E[X] in this case = $\displaystyle \lambda$
    Hey there Jan!

    Try reading this thread: http://www.mathhelpforum.com/math-he...-one-more.html

    Then let me know if you're still stuck.
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  3. #3
    Bar0n janvdl's Avatar
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    Quote Originally Posted by mr fantastic View Post
    Hey there Jan!

    Try reading this thread: http://www.mathhelpforum.com/math-he...-one-more.html

    Then let me know if you're still stuck.
    Thanks Mr F, I have some sort of idea now
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