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Homework Help: Variance and Expected Value Problem

  1. Oct 11, 2011 #1
    Give an example of a random variable (i.e. give the range of values it takes and its p.m.f.) with the following properties: EX = 4, VAR(X)=4. Now give an example of a random variable with a different p.m.f. than the first one you gave, but that still has EX = 4, VAR(X)=4.

    So this means then E(X) = E(X^2) - (E(x))^2 right?
    I'm not sure if this is the way I should approach the problem?
  2. jcsd
  3. Oct 12, 2011 #2


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    Not really. They just happen to equal the same number. What I would do is first find a random variable A with a mean of 0 and variance of 4. Then the variable B=A+4 will have a mean of 4 and a variance of 4.
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