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Math Help - Standard Deviation and Varians

  1. #1
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    Standard Deviation and Varians

    I first of all apologize if this is the wrong category. This is for a Statics class at college level, but basic statistics.

    I am really having a hard time and confusing myself when it comes to the standard deviation and variations. The formulas (do the best I can without the keys needed on the keyboard) are:

    O2m = O2 squared / N - this is variance

    Om = this is standard deviation (standard deviation / N squared = standard deviation)

    When given a problem are we be given one or the other to calcuate and then continue with the rest of the steps. For example if I am given the standard deviation of 8 and my N = 10 then 8/10 = .80 so this would be my standard deviation.

    Would I also then calcuate a variance or or is that only if you are given the variance in the problem you would then use the formula to determine your variance.

    This is the only part I am having a really hard time grasping. Ugh.

    Thanks for your help!!
    Last edited by nursetobe; March 31st 2010 at 02:25 PM. Reason: information backwards
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  2. #2
    MHF Contributor matheagle's Avatar
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    Hello Nurse Toby.

    The problem seems to be the terminology
    Let \sigma^2 be the variance of one observation whether thats X_1 or X_2....
    It's the variance of each one of them.

    NOW the sample mean is \bar X={X_1+...+X_n\over n}

    and the variance of \bar X is \sigma^2/n

    and the st deviation of \bar X is \sigma/\sqrt{n}
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  3. #3
    Super Member Anonymous1's Avatar
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    Quote Originally Posted by nursetobe View Post
    This is for a Statics class at college level
    Statics??? I thought you wanted to be a nurse, not an engineer.

    Quote Originally Posted by matheagle View Post
    Hello Nurse Toby.
    hahahaha
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  4. #4
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    Thanks for your help matheagle

    Anonymously, trust me if it were up to me I wouldn't be taking statistics but it is required for a BSN!!

    Great site by the way!!!
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  5. #5
    MHF Contributor matheagle's Avatar
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    You're welcome, my friends call me the beagle, short for mathbeagle my alter ego
    I solve math problems during the day and fight crime at night
    no wait, it's the other way around
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