$\begin{align}  & mean=\bar{x}=\frac{2+4+7+8+9}{5} \\ & \bar{x}=\frac{30}{5}=6 \\ & variance={{\sigma }^{2}} \\ & {{\sigma }^{2}}=\frac{{{\left| 2-6 \right|}^{2}}+{{\left| 4-6 \right|}^{2}}+{{\left| 7-6 \right|}^{2}}+{{\left| 8-6 \right|}^{2}}+{{\left| 9-6 \right|}^{2}}}{5} \\ & {{\sigma }^{2}}=\frac{16+4+1+4+9}{5}=\frac{34}{5}=6.8 \\\end{align}$