Answer
$\approx0.82$
Work Step by Step
The mean of $n$ numbers is the sum of the numbers divided by $n$.
Hence the mean: $\frac{2\cdot8+3\cdot9+2\cdot10}{7}=9$
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: $\sqrt{\frac{2(8-9)^2+3(9-9)^2+2(10-9)^2}{7-1}}\approx0.82$
