Question

The mean deviation from mean of observations $5,10,15,20,.........85$ is :-

• A. 43.71
• B. 21.17
• C. 38.7
• D. None of these

Answer 1

Answer: (B)

$\because$ M.D. from mean of the series
$a,a+d,a+2d,\dots .,a+2nd$ is
M.D. $=\frac{n(n+1)}{2n+1}|d|$
for given series $5,10,15,\dots \dots ,85$
$a=5,d=5,a+2nd=85$
i. e. $n=8$
$\therefore \text{ M.D. }=\frac{8\times 9}{17}5=21.17$