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Math Help - [SOLVED] Finding the Mean / Variance / Standard Deviation

  1. #1
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    [SOLVED] Finding the Mean / Variance / Standard Deviation

    I'm having a hard time trying to figure out how to start off on this problem. so the question asks:

    "The Bureau of Land Management did a study of the water table near Custer, Wyoming, in the month of June. Based on data from the Bureau, a random sample of 20 water wells showed that the distances from the ground to the water level (in feet) were

    Distance from the ground to water level:12-14 | 15-17 | 18-20 | 21-23 | 24-26
    Number of Wells f: 1 | 3 | 8 | 2 | 6

    would I start off by finding the mean of each value from "Distance from the ground to water level"? Such as (12+13+14)/3=13 would be the mean for 12-14?
    then 1(13)+ the rest?

    or am i supposed to do something else

    The question asks to find:
    a. Sample Mean
    b. Sample Variance
    c. Sample Standard Deviation

    EDIT: I think the 12-14, etc are categories, which the other numbers are frequencies. If that's the case, I may know how to solve this. It'd be great if anybody can confirm this.
    Last edited by fb280; February 15th 2010 at 05:43 PM.
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  2. #2
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    It is a frequency table; there is nothing else it can be. As you get further into your class you'll understand why. You should have a formula in your notes for computing the mean of a frequency table. It is however pretty intuitive. Same for variance and standard deviation.
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  3. #3
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    ok thanks, i just needed someone to verify this for me.
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