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Math Help - Calculate E[X] and Var[X]

  1. #1
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    Calculate E[X] and Var[X]

    Question : Calculate E[X] and Var[X] when X represents the outcome when a fair die is rolled.
    ---------------------------------------------------------------------

    Pr(X) = \frac{1}{6}

    E[X] = \sum_{x=1}^{6} x f(x)

    Var[X] = E[(X- \mu)^2]
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  2. #2
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    Quote Originally Posted by zorro View Post
    Question : Calculate E[X] and Var[X] when X represents the outcome when a fair die is rolled.
    ---------------------------------------------------------------------

    Pr(X) = \frac{1}{6}

    E[X] = \sum_{x=1}^{6} x f(x)

    Var[X] = E[(X- \mu)^2]
    Substitute f(x) and the values of x into the formulas that you have quoted and do the calculations.

    Please show all your work if you're still stuck.
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  3. #3
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    I am getting the following results

    E[X] = \frac{10}{3}

    Var[X] = 3.07 .................Is that correct???
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  4. #4
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    E(x)=3.5
    Last edited by matheagle; December 31st 2009 at 11:02 AM.
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  5. #5
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    Quote Originally Posted by zorro View Post
    Question : Calculate E[X] and Var[X] when X represents the outcome when a fair die is rolled.
    ---------------------------------------------------------------------

    Pr(X) = \frac{1}{6}

    E[X] = \sum_{x=1}^{6} x f(x)

    Var[X] = E[(X- \mu)^2]

    i think you should try to make a probability
    x | f(x)
    1 | 1/6
    2 | 1/6
    : | :
    : | :
    6 | 1/6

    then use the formula:
    E[X] = \sum_{x=1}^{6} x f(x)
    E[X] = 1. f(1)+ 2. f(2)+.....+ 6. f(6)

    hope it help....
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  6. #6
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    Quote Originally Posted by zorro View Post
    I am getting the following results

    E[X] = \frac{10}{3}

    Var[X] = 3.07 .................Is that correct???
    I think you know now that the first is not correct (I haven't checked the second).

    When I say:
    Please show all your work if you're still stuck.
    I don't mean that you simply show the results of your work. I mean show all the work. If you had done this, it (probably) would have been simple to point out the mistake you made. Post #5 shows what I expected you to post when I said:
    Substitute f(x) and the values of x into the formulas that you have quoted and do the calculations
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  7. #7
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    thanks mite
    cheers
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