Question

The mean deviation of the numbers 3, 4, 5, 6, 7 from the mean is
(a) 25
(b) 5
(c) 1.2
(d) 0

Answer 1

(c) 1.2

$$\begin{gathered} \mathrm{Mean}\left(\overline{X}\right)=\frac{3+4+5+6+7}{5} \\ =\frac{25}{5} \\ =5 \end{gathered}$$
Taking the absolute value of deviation of each term from the mean, we get:

$$\begin{gathered} \mathrm{MD}=\frac{\left|(3-5)\right|+\left|(4-5)\right|+\left|(5-5)\right|+\left|(6-5)\right|+\left|(7-5)\right|}{5} \\ =\frac{2+1+0+1+2}{5} \\ =\frac{6}{5} \\ =1.2 \end{gathered}$$