Solution:

$X_{i}$	$d_{I}=x_{I}-\bar{x}$	$|d_{i}|$
3	-6.5	6.5
5	-4.5	4.5
6	-3.5	3.5
7	-2.5	2.5
10	0.5	0.5
12	2.5	2.5
15	5.5	5.5
18	8.5	8.5
$(\sum x_{i}=76$		$\sum\left|d_{i}\right|=34$

where Mean $\overline{x}=\frac{\sum x_{i}}{N}=\frac{76}{8}$$ \begin{aligned} \overline{x}=9.5 \ \text { Mean deviation about mean } &=\frac{\sum\left|d_{i}\right|}{N} \ &=\frac{34}{8}=4.25 \end{aligned} …