To compute the mean, you simply have to sum all the elments in the data set and the divide the sum by the number of elements:
To compute the variance, we first need to compute the distance of each element from the mean. To do so, we build a "parallel" dataset, given by the difference of every value and the mean:
Now we need those difference squared:
The variance is the mean of this new vector, so
Finally, the standard deviation is simply the square root of the variance, so you have
