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Math Help - Normal Distribution Problem

  1. #1
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    Normal Distribution Problem

    Got my AS level stats test soon and do not understand one of the past paper questions.


    The Distances travelled to work, Dkm, by the employeed at a large company are normally distributed with D-N(30,82) ..... so mean of 30 and variance of 82?
    Find the probability that a randomly selected employee has a journey to work of more than 20km.

    The mark scheme says

    P(D > 20) = P(Z > 20-30/8)
    Where did they get the divide by 8 from? I thought it was sqrt(82)

    Any help would be great thanks.
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  2. #2
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    Re: Normal Distribution Problem

    It can't be 8, you are correct it should be \sqrt {82}
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