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Math Help - standard deviation

  1. #1
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    standard deviation

    There are 3000 cars travelling between St.Paul and McGregory each day. 38% is the probability that a motorist is speeding on this highway. Calculate the standard deviation for the number of cars

    sd = sqr(nxpx1-p)

    I know the answer is 26.59 but I don't get this answer.

    Please help
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  2. #2
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    n= the number of cars = 3000, p = the probability of a car speeding.

    sd = \displaystyle \sqrt{np(1-p)}= \sqrt{3000\times .38\times (1-.38)} = 26.59
    Last edited by pickslides; January 16th 2011 at 12:07 PM. Reason: bad latex
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    Thanks.
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