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Math Help - expected value with variables!

  1. #1
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    Exclamation expected value with variables!

    first part:

    A box contains 7 black cubes and 3 red cubes. Debra selects three cubes from the box without replacement. Let random variable N denote the number of red cubes selected by Debra.

    second part:

    Debra will win $2.00 for every red cube selected and lose $1.00 for every black cube selected. Let the random variable W denote Debra's winnings.
    If W=aN+b, find a and b. Hence, find E(W)



    ---------------------------------

    I'm okay with the first part ...but I'm not sure how to approach the second part.


    Help please!
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  2. #2
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    Quote Originally Posted by shawli View Post
    first part:

    A box contains 7 black cubes and 3 red cubes. Debra selects three cubes from the box without replacement. Let random variable N denote the number of red cubes selected by Debra.

    second part:

    Debra will win $2.00 for every red cube selected and lose $1.00 for every black cube selected. Let the random variable W denote Debra's winnings.
    If W=aN+b, find a and b. Hence, find E(W)



    ---------------------------------

    I'm okay with the first part ...but I'm not sure how to approach the second part.


    Help please!
    W = (2)(N) - (1)(3 - N) = ....

    E(aN + b) = a E(N) + b.
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