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Math Help - Binomial Distribution Question

  1. #1
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    Binomial Distribution Question

    The random variable X has the distribution B (n, 0.1). Given that the mean and standard deviation of X are equal, find the value of n. [5]

    The only things I could work out were:

    E(X)(mean) = n x 0.1
    SD(X) = root of VAR(X)
    VAR(X) = n x 0.1 x 0.9
    VAR(X) = n x 0.09

    n x 0.1 = root of 0.09 x n

    What happens from here? Is it meant to be solved in a different way?
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  2. #2
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    Quote Originally Posted by db5vry View Post
    The random variable X has the distribution B (n, 0.1). Given that the mean and standard deviation of X are equal, find the value of n. [5]

    The only things I could work out were:

    E(X)(mean) = n x 0.1
    SD(X) = root of VAR(X)
    VAR(X) = n x 0.1 x 0.9
    VAR(X) = n x 0.09

    n x 0.1 = root of 0.09 x n

    What happens from here? Is it meant to be solved in a different way?
    Guess you are on the right track.
    square your equation to get:

    0.01n^2=0.09n

    0.01n^2-0.09n=0

    n(0.01n-0.09)=0

    \text{n=0 (N.A) or n=9}
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