standard deviation is the positive square root of mean of the deviations from an arithmatic mean X denoted as sigma.
sigma=sqrt {(sum(x-X)^2)/n}
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Square the standard deviation and you will have the variance.
You need more than one number to calculate a standard deviation, so 9 does not have a standard deviation.
Standard deviation = square root of variance.
Standard deviation is how much a group deviates from the whole. In order to calculate standard deviation, you must know the mean.
In the same way that you calculate mean and median that are greater than the standard deviation!