Answer
The variance:
$s^2=36$
The standard deviantion:
$s=6$
Work Step by Step
At first, let's evaluate the sample mean:
$x̅=\frac{20+13+4+8+10}{5}=11$
Now, the variance:
$s^2=\frac{Σ(x_i-x̅^2)}{n-1}=\frac{(20-11)^2+(13-11)^2+(4-11)^2+(8-11)^2+(10-11)^2}{5-1}=\frac{81+4+49+9+1}{4}=36$
The standard deviantion:
$s=\sqrt {36}=6$
