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Math Help - Normal Distribution HELP!

  1. #1
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    Post Normal Distribution HELP!

    Hello, I don't understand how the NORMAL DISTRIBUTION column of the attached chart is calculated, can someone please explain?

    The mean is 40 and the Standard Deviation is 10

    Normal Distribution HELP!-table.png
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  2. #2
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    Re: Normal Distribution HELP!

    The 68,95,99.7 rule may come in handy to help your understanding...
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  3. #3
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    Re: Normal Distribution HELP!

    For the row 20<30 they find what percent of the population lies between 20 and 30 in a normal distribution. If you look at a normal distribution table like this one Standard Normal Distribution Table
    you can see what percent is between a given number of standard deviations from the mean.
    20 is 2 standard deviations below the mean \frac{20-40}{10}=-2 and 30 is 1 standard deviations below the mean \frac{30-40}{10}=-1
    From the table you can see that 34.1% lies between the mean and 1 standard deviation below the mean. Also 47.7% lies between the mean and 2 standard deviations below the mean. Therefore 47.7-34.1= 13.6% lies between 1 and 2 standard deviations below the mean. 13.6% is the 0.1359 figure in the table.
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