GCSE Statistics - standard deviation h/w

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Recall that the standard deviation is defined as the square root of variance. The variance for a discrete random variable $X$ of $n$ equally likely values is given by

$\displaystyle var(X) = \frac{1}{n} \sum_{i=1}^n (x_i - \mu)^2 = \bigg( \frac{1}{n} \sum_{i=1}^n x_i ^2 \bigg) - \mu^2$

where $\displaystyle \mu = \frac{1}{n} \sum_{i=1}^n x_i$ is the mean.

The sums being taken over all values of $x$.

You have been given the sum of squares of the scores and the sum of scores, simply use this information directly to evaluate what you need.

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