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Math Help - [SOLVED] Probability distribution

  1. #1
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    [SOLVED] Probability distribution

    Random variable X has probability distribution

    x_______________1________2_______3________4_______ 5
    P(X=x)________0.10_____0.15_____0.20_____0.25_____ 0.30

    E(X)= 3.5

    Var(X)= 0.95

    Find Var(3-2X)

    Please help!
    Last edited by mr fantastic; May 5th 2009 at 06:57 AM. Reason: Merged posts
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  2. #2
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    Quote Originally Posted by greghunter View Post
    sorry that didn't work

    Random variable X has probability distribution

    x_______________1________2_______3________4_______ 5
    P(X=x)________0.10_____0.15_____0.20_____0.25_____ 0.30

    E(X)= 3.5

    Var(X)= 0.95

    Find Var(3-2X)

    Please help!
    Use Var(aX + b) = a^2 Var(X).

    Note: I haven't checked your calculations for E(X) and Var(X).
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  3. #3
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    Quote Originally Posted by greghunter View Post
    sorry that didn't work

    Random variable X has probability distribution

    x_______________1________2_______3________4_______ 5
    P(X=x)________0.10_____0.15_____0.20_____0.25_____ 0.30

    E(X)= 3.5

    Var(X)= 0.95

    Find Var(3-2X)

    Please help!
    E(X)= (1)(0.10) + (2)(0.15) + (3)(0.20) + (4)(0.25) + (5)(0.30)=3.5

    E(X^2)= (1)(0.10) + (4)(0.15) + (9)(0.20) + (16)(0.25) + (25)(0.30)=14

    Var(X) \textrm{ should be } 14-3.5^2=1.75

    After that just solve accordingly
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