$\begin{align}  & mean=\overline{x}=\frac{2+3+8+10+12}{5}=\frac{35}{5}=7 \\ & v=\frac{{{(2-7)}^{2}}+{{(3-7)}^{2}}+{{(8-7)}^{2}}+{{(10-7)}^{2}}+{{(12-7)}^{2}}}{5} \\ & variance=\frac{25+16+1+9+25}{5}=\frac{76}{5}=\text{15}\text{.2} \\ & standard deviation=\sqrt{variance}=\sqrt{15.2} \\ & standard deviation=\sigma \approx \text{3}\text{.9  (1d}\text{.p)} \\\end{align}$