Mean deviation from the mean for data 6, 7, 10, 12, 13, 4, 8, 12 is

$$\begin{gathered} Mean=\frac{6+7+10+12+13+4+8+12}{8}=\frac{72}{8}=9 \\ \mathrm{Mean} \mathrm{deviation} \mathrm{about} \mathrm{mean}=\frac{1}{\mathrm{n}}\sum _{\mathrm{i}=1}^{\mathrm{n}} \left|{\mathrm{x}}_{\mathrm{i}}-\overline{\mathrm{x}}\right| \\ =\frac{\left|6-9\right|+\left|7-9\right|+\left|10-9\right|+\left|12-9\right|+\left|13-9\right|+\left|4-9\right|+\left|8-9\right|+\left|12-9\right|}{8} \\ =\frac{3+2+1+3+4+5+1+3}{8}=\frac{22}{8}=2.75 \end{gathered}$$