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Math Help - Variance, Number of Heads and Tails

  1. #1
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    Variance, Number of Heads and Tails

    Hello,
    I was just reviewing some discrete probability problems and came across this one. Not sure how to do it...

    Let Xn be the random variable that counts the difference in the number of tails and the number of heads when n coins are flipped.
    a) What is the expected value of Xn?
    b) What is the variance of Xn?
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  2. #2
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    Quote Originally Posted by discprobques View Post
    Hello,
    I was just reviewing some discrete probability problems and came across this one. Not sure how to do it...

    Let Xn be the random variable that counts the difference in the number of tails and the number of heads when n coins are flipped.
    a) What is the expected value of Xn?
    b) What is the variance of Xn?
    The difference can defined by D = |n - 2X| where n ~ Binomial(n, 1/2). So you could start by constructing a partial probability table and calculating E(D) and Var(D) in the usual way.
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