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Math Help - Normal distribution

  1. #1
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    Normal distribution

    I am drawing a blank on how to solve this problem. Can somebody help?
    "A normal distribution consist of 100 scores with a mean of 65 and a standard deviation of 5. How many scores are above 70 and how many are below 55?
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by graceofayak View Post
    I am drawing a blank on how to solve this problem. Can somebody help?
    "A normal distribution consist of 100 scores with a mean of 65 and a standard deviation of 5. How many scores are above 70 and how many are below 55?
    Badly posed question, the scores may have a normal distribution with mean
    65 and SD of 5, but the numbers above 70 and below 55 are random
    variables, and so not fixed numbers. We can talk of the percentage of scores
    above 70 and below 55, but these will not be the number out of a sample of
    100 that are above and below these values (well not often anyway).

    RonL

    (70 is 1 SD above the mean so looking 1 up in a table of the standard normal
    distribution we find 84.13% of scores are below 70, and so 15.87% are above
    70. Similarly 55 is 2 SD's below the mean so looking -2 up in the table of the
    cumulative standard normal distribution we see that 2.28% of scores are less
    than 55.)
    Last edited by CaptainBlack; June 17th 2007 at 11:31 AM.
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