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

$Mean\overline{x}=\frac{\Sigma f_i{x}_i}{\Sigma h}=\frac{18+40+105+225+88+52}{4+8+15+25+8+4}$

$=\frac{521}{66}=8$

Now prepare the table given below :

$\Sigma h=66,\Sigma f_i|x_i-\overline{x}|=138$

$\therefore \text{\hspace{0.17em}Mean\hspace{0.17em}deviation\hspace{0.17em}}=\frac{{\displaystyle \sum _{i=1}^6{f}_i|x_i-\overline{x}|}}{\Sigma f_i}=\frac{138}{66}=2.09$