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Q.
The mean deviation from mean of observations
$5, 10, 15, 20, .........85$ is :-
Statistics
Solution:
$\because$ M.D. from mean of the series
$a , a + d , a +2 d , \ldots ., a +2 nd$ is
M.D. $=\frac{ n ( n +1)}{2 n +1}| d |$
for given series $5,10,15, \ldots \ldots, 85$
$a =5, d =5, a +2 nd =85$
i. e. $n =8$
$\therefore \text { M.D. }=\frac{8 \times 9}{17} \quad 5=21.17$