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Math Help - Using the Normal Distribution as a Model for Individual Measurements

  1. #1
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    Using the Normal Distribution as a Model for Individual Measurements

    The cross-sectional area of plastic tubing for use in pulmonary resuscitators is normally distributed with mean 12.5 mm^2 and standard deviation 0.2 mm^2. When the area is less than 12.0 mm^2 or greater than 13.0 mm^2, the tube does not fit properly. If the tubes are shipped in boxes of 1000, how many wrong-sized tubes per box can doctors expect to find?

    Thanks!
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  2. #2
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    Joined
    May 2010
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    Question

    z=(x-mean)/standard dev

    so

    z1=(13-12.5)/0.2

    z2=(12-12.5)/0.2

    look up z1 and z2 in the normal distribution tables.

    Use these to find
    P(x<z1)=P(x<13)
    P(x<z2)=P(x<12)

    Then P(x<13)-P(x<12) = P(12<x<13)

    Multiply by 1000

    Should work a treat.


    -Do you get 68 wrong sized tubes?
    Last edited by yccmp; May 6th 2010 at 03:16 AM.
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