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DIY Maths: Range, variation and standard deviation
Mathsisfun.com does a good job of explaining how to find variance and standard deviation. At the end of this page, you will find a quiz to test your knowledge. For a more advanced discussion, see www.onlinemathlearning.com/variance.html.
Make a list of numbers (a data set) and use this online calculator to find the standard deviation of the set. Compare the calculator's answer to your own worked-out answer to see if you have it right.
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measures of dispersion range, variance and standard deviation