Standard deviation s
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The standard deviation is the positive square root of the variance, i.e. s = √V. Thus, if the variance has units of cows^{2}, the standard deviation has units of cows, the same as the variable x. The standard deviation is therefore more popularly used to express a measure of spread.
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The variance V of the Uniform(1,3) distribution is calculated as follows:

 from here 
and therefore
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V=\frac{26}{6}2^2=\frac{1}{3} 
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and the standard deviation s is therefore:
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\sigma=\sqrt V= \frac{1}{\sqrt 3} 
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Variance and standard deviation have the following properties, where a is some constant and X, Xi are random variables:
 and 

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 providing the Xis are uncorrelated. 
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