Mathematics - Statistics Question with Solution | TestHub

$\begin{array}{rl}& 8+(n-1)13=320\\ & 13n=325\\ & n=25\\ & \text{ no. of terms }=25\end{array}$ $\begin{array}{rl}& \text{ mean }=\frac{\sum {\mathrm{x}}_{\mathrm{i}}}{\mathrm{n}}=\frac{8+21+\dots +320}{25}=\frac{\frac{25}{2}(8+320)}{25}\\ & \text{ variance }{\sigma }^2=\frac{\sum {\mathrm{x}}_{\mathrm{i}}^2}{\mathrm{n}}-(\text{ mean }{)}^2\\ & =\frac{8^2+21^2+\dots .+320^2}{13}-(164{)}^2\\ & =8788\end{array}$