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# S1 edexcel standard deviation formula? Watch

1. On page 60 of heinemann edexcel S1 there is a formula for the best estimate of the standard deviation of a sample......

(1/(n - 1))(sum (x^2) - ((sum (x))^2)/n)

and they have practice questions on this. I've looked through past papers and i've never seen this formula used for finding standard deviation estimates of 'samples'.

I'm kind of confused as to when I should be using this formula, if at all. Is there a possibility it will be required in the exam?
2. Ignore it - you don't need to know this formula for Edexcel S1
3. That's an S2 formula for finding an unbiased estimator for the standard deviation; you won't need it in S1.
4. I've done S1 twice already (and today for the third time lol) and we're told to do 'the mean of the squares minus the square of the mean'.
That is ?((x^2)/n)-(?(x/n))^2
Or at least it's something like that

Updated: May 20, 2011
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