Standard Deviation

Here is the formula:

$\sqrt{\frac{\Sigma {\left(x-m\right)}^2}{n-1}}$

Where x is the value being worked out,
m is the mean of the data
n is the number of values.

The brackets after the Σ needs to be done for every single value, then added up.

For Example:

1. $\mathrm{23}-\mathrm{Some\; mean\; value}=\mathrm{12}$
2. $\mathrm{24}-\mathrm{Some\; mean\; value}=\mathrm{24}$
3. $\mathrm{25}-\mathrm{Some\; mean\; value}=\mathrm{36}$
4. $\mathrm{26}-\mathrm{Some\; mean\; value}=\mathrm{48}$
5. $\mathrm{27}-\mathrm{Some\; mean\; value}=\mathrm{60}$
6. $\mathrm{28}-\mathrm{Some\; mean\; value}=\mathrm{72}$
7. $\mathrm{29}-\mathrm{Some\; mean\; value}=\mathrm{84}$
8. $\mathrm{30}-\mathrm{Some\; mean\; value}=\mathrm{96}$
9. $\mathrm{31}-\mathrm{Some\; mean\; value}=\mathrm{108}$

And the total is 540

So, that then completes the top of the formula, then you complete and tada!

You should now have this done and ready to go ;)