16, 21, 21, 22, 22, 23, 24, 24, 25, 25, 25, 25, 26, 26, 26, 26, 27, 27, 28, 20, 29, 29, 31, 32, 33, 33, 35, 35, 36, 37
$\displaystyle \sigma ^2 = \frac{1}{N} \sum_{n = 1}^N (\bar{x} - x_n)^2$ <-- variance
where $\displaystyle \bar{x} = \frac{1}{N} \sum_{n = 1}^Nx_n$
and
$\displaystyle \sigma = \sqrt{\frac{1}{N} \sum_{n = 1}^N (\bar{x} - x_n)^2}$ <-- standard deviation
Depending on the kind of statistic you are trying to work with the $\displaystyle \frac{1}{N}$ might be a $\displaystyle \frac{1}{N - 1}$. You'll have to check your text or your notes to make sure.
So the first thing to is to calculate the average, $\displaystyle \bar{x}$, then use that to find the variance.
-Dan
Take a look at the symbol I used for the variance, $\displaystyle \sigma ^2$. (This may not be a Universal notation, but it is standard in the two books I own.)
So to get the standard deviation $\displaystyle \sigma$ from the variance, just take the square root.
-Dan