Using step-deviation method, calculate the mean marks of the foll… - Vidyadip

Question

Using step$-$deviation method, calculate the mean marks of the following distribution

Class Interval	$50 - 55$	$55 - 60$	$60 - 65$	$65 - 70$	$70 - 75$	$75 - 80$	$80 - 85$	$85 - 90$
Frequency	$5$	$20$	$10$	$10$	$9$	$6$	$12$	$8$

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Answer

$\therefore \text { Mean } X = A +\frac{\sum f \cdot u}{\sum f} \times i .[ i =\text { length of C.I. }]$
$=67.5+\frac{24}{80} \times 5$
$=67.5+1.5$
$=69 .$

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