The mean deviation (approximately) from the mode for the data, is 20, 25, 30, 18, 15, 40

We have,

Mean $=\frac{20+25+30+18+15+40}{6}=\frac{148}{6}$

Median $=\frac{20+25}{2}=\frac{45}{2}$

$\therefore$ Mode = 3 Median -2 Mean $=\frac{135}{2}-\frac{148}{3}=\frac{109}{6}$

Hence, mean deviation about mode is given by 

$\begin{array}{l}\frac{\left|20-\frac{109}{6}\right|+\left|25-\frac{109}{6}\right|+\left|30-\frac{109}{6}\right|+\left|18-\frac{109}{6}\right|+\left|15-\frac{109}{6}\right|+\left|40-\frac{109}{6}\right|}{6}\\ \text{ M.D. }=\frac{11+41+71+1+19+131}{36}=\frac{274}{36}=7.61\\ \end{array}$