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Math Help - How to do probability >-<

  1. #1
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    How to do probability >-<

    Jerseys will sell for $30. Random variable X is number of jerseys that will be sold. E(X)=100 and R is the total revenue (R=30X). What is the expected revenue.

    I have no idea what formula to use. I thought conditional probability because revenue is dependent on the sale of the jerseys, but the formula does not match my data, or I am writing it back the front.

    Why is it not $3000...?

    I think if I knew the formula I could work it out~ maybe :-)
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by char111 View Post
    Jerseys will sell for $30. Random variable X is number of jerseys that will be sold. E(X)=100 and R is the total revenue (R=30X). What is the expected revenue.

    I have no idea what formula to use. I thought conditional probability because revenue is dependent on the sale of the jerseys, but the formula does not match my data, or I am writing it back the front.

    Why is it not $3000...?

    I think if I knew the formula I could work it out~ maybe :-)
    Definition of the expectation of a function of a RV:

    E(f(X))=\int f(x) p_X(x)\; dx

    so:

     <br />
E(30X)=\int 30\; x\; p_X(x)\;dx=30 E(X) <br />

    where the integrals are over the support of p_X.

    Make the obvious modification or interpretation for a discrete RV.

    CB
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  3. #3
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    Thanks Captain Black~ obviously I have no idea because I have not seen this formula before in class nor can I find it in my book.

    100 x (30x100)...is that how I plug in my numbers...?

    This topic just confuses me the more I try to understand it~ give me SPSS anytime :-)
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