Find the mean deviation about the mean for the following data :

We have,

Therefore, $\overline{\mathrm{X}}=\frac{\sum_{\mathrm{i}=1}^{6} \mathrm{f}_{\mathrm{i}} \mathrm{x}_{\mathrm{i}}}{\sum_{\mathrm{i}=1}^{6} \mathrm{f}_{\mathrm{i}}}=\frac{528}{66}=8$

Now,

Thus, the required mean deviation about the mean is

M. $D(\bar{x})=\frac{\sum_{i=1}^{6} f_{i}\left|x_{i}-\bar{x}\right|}{\sum_{i=1}^{6} f_{i}}=\frac{138}{66}=2.09$