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    For standard deviation and variance there seems to be 2 formulae. One for populations, the normal one, and then theres the one for samples where u divide by n-1... But I was never taught this one at school or seen it in any oither books/ mark scheemes, so should i learn it?
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    Me neither and i keep getting questions wrong. I'm still not sure when to use each one
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    What are you,guys, talking about? There is only one formula for sd:

    sd= square root of (fx^2/n + mean^2)

    sd^2=variance

    BTW, I'm doing OCR MEI...edexcel may be different.
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    dont you subtract the mean squared, not add it!?
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    (Original post by Willa)
    dont you subtract the mean squared, not add it!?
    Thats right
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    Does nobody know which formula to use at what times?? Its annoying!
 
 
 
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Updated: June 10, 2004
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