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Math Help - Expectation of a Variable

  1. #1
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    Expectation of a Variable

    dice has faces numbered 1 to 6 and is weighted so that the probability of
    throwing n (n = 1; 2; :::; 6) in a single throw is proportional to n, i.e., equals
    Cn for some constant C.
    (a) Find C .
    (b) Let X be equal to the number shown when the dice is thrown.
    i) Compute E(X^3).
    I've calculated C as 1/21.

    However, i thought the expectation of E(x^3) would thus be:


    E(X^3) = n^3/21
    so: 1/21 + 2^3/21 + 3^3/21 etc....

    EDIT: Is Latex now working? I keep getting errors whilst using it.

    Thankyou
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  2. #2
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    Use the TEX tags instead of the MATH tags, for now. Personally, i don't know hte difference, except that one works.

    Let's try that Expectation again.

    p(1) = 1/21
    p(2) = 2/21
    p(3) = 3/21
    etc.

    E(X^3) = 1*p(1) + 8*p(2) + 27*p(3) + ... + 216*p(6) -- There aren't any 'n's left in there.
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