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Math Help - Find the Mean

  1. #1
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    Find the Mean

    If X is a normal variable with a standard deviation of 2 and Pr(X<9) = 0.8
    Find the mean.

    Im new to the whole normal distribution thing so i would really appreciate some help.

    thanks
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  2. #2
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    Quote Originally Posted by Kash View Post
    If X is a normal variable with a standard deviation of 2 and Pr(X<9) = 0.8
    Find the mean.

    Im new to the whole normal distribution thing so i would really appreciate some help.

    thanks
    Find the value z* of Z such that Pr(Z < z*) = 0.8.

    Substitute this value into Z = \frac{X - \mu}{\sigma}:

    z* = \frac{9 - \mu}{2}.

    Solve for \mu.
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  3. #3
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    wow i didnt know that formula!, thanks alot!
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