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Math Help - Standard Normal Distribution

  1. #1
    Newbie Leezard's Avatar
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    Nov 2008
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    Wetaskiwin, AB
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    Standard Normal Distribution

    Hello!

    I'm not a math whiz. Wasn't in high school, and definitely not now. Especially since they have completely revamped the Math 33 curriculum -- this is stuff we didn't TOUCH in high school!

    Anyways, probability is one of the worst. I've tried this over and over again and just cannot find the conclusion. If you could not only help me solve the problem, but walk me through step-by-step (treat me like an idiot, and maybe I"ll understand). Thank you SO much!!

    Bean plants in a field have heights that are normally distributed, with a mean of 20.0 cm and a standard deviation of 3.5 cm. Find the proportion of plants that are between 15.8 cm and 24.2 cm tall.

    So if z=x-u/o then:
    z=15.8-20/3.5
    z=-4.2/3.5
    z=-1.2
    which, according to the z-score table, equates to 0.0985

    Alternatively:
    z=24.2-20/3.5
    z=4.2/3.5
    z=1.2
    which, according to the godly table, equates to 0.8849

    Have I done this right so far? If so, this is where I get lost.... according to my textbook, I'm supposed to subtract 0.0985 from 0.8849, which is 0.7864.

    The answer is 0.7699.

    Where have I gone wrong? Thanks so much for helping!!
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  2. #2
    Newbie Leezard's Avatar
    Joined
    Nov 2008
    From
    Wetaskiwin, AB
    Posts
    2
    I figured out the problem.

    I was reading the chart wrong. Boy, I feel dumb, but SO much better that I had the theory right!!

    Back to work. Thanks anyways.
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