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badboy killa
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#1
Report Thread starter 16 years ago
#1
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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Rrrrob
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#2
Report 16 years ago
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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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maljosh
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#3
Report 16 years ago
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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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Willa
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#4
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dont you subtract the mean squared, not add it!?
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Greendaygirl
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#5
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(Original post by Willa)
dont you subtract the mean squared, not add it!?
Thats right
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badboy killa
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#6
Report Thread starter 16 years ago
#6
Does nobody know which formula to use at what times?? Its annoying!
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