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Homework Help: Find the probability from the expected value?

  1. Apr 17, 2012 #1
    1. The problem statement, all variables and given/known data

    z = 2, P(Z=z)=1/6

    z = 3, P(Z=z)=1/6

    z = 5, P(Z=z)=1/6

    z = 7, P(Z=z)= x

    z = 11, P(Z=z)= y

    I'm supposed to find x and y given that E(Z)= 5+2/3

    I have no idea how to do this. All I got is 7x+11x=4 but I can't solve this
  2. jcsd
  3. Apr 17, 2012 #2


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    I think you mean you got 7x+11y = 4. To get another equation remember that the Z probabilities must add to 1.
  4. Apr 18, 2012 #3
    Thanks A LOT! How did I not think of that? :-)
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