Answer
$\approx1.58$
Work Step by Step
The mean of $n$ numbers is the sum of the numbers divided by $n$.
Hence the mean: $\frac{16+17+18+19+20 }{5}=18$
The standard deviation of $x_1,x_2,...,x_n$ is (where $\overline{x}$ is the mean of the data values): $\sqrt{\frac{(x_1-\overline{x})^2+(x_2-\overline{x})^2+...+(x_n-\overline{x})^2}{n-1}}$.
Hence here the the standard deviation is: $\sqrt{\frac{(16-18)^2+(17-18)^2+(18-18)^2+(19-18)^2+(20-18)^2}{5-1}}\approx1.58$
