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Math Help - Standard deviation

  1. #1
    Junior Member
    Joined
    Oct 2009
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    30

    Unhappy Standard deviation

    I'm sorry if I posted in the wrong section. (If I did tell me what section it's supposed to go) Anyways, how do I find the standard deviation of something when I only know the average and the amount of "tests" there were.

    Like take this question for example: 300 equal samples were taken from a lake. 225 of the samples were in the pH range from 5.5 to 6.5. The mean pH is 6.0. What is the standard deviation?

    Also, if there happens to be a way, let me know if I can somehow do this on a calculator program (TI-83 Plus).

    Thank you.
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  2. #2
    Super Member Anonymous1's Avatar
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    Do you have the data?

    Sample standard deviation:

    s= \sqrt{\frac{1}{n-1}\sum(x_i - \mu)^2}
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