Find the mean of the following distribution ...

ICSE Class X Math 2013 Paper

Question : 37 of 46

Marks: +1, -0

Find the mean of the following distribution by step deviation method:

Class Interval	20-30	30-40	40-50	50-60	60-70	70-80
Frequency	10	6	8	12	5	9

Solution:

C.I.	Frequency $(f_i)$	Mid-value(x)	$d_i= \;\frac{x-a}{h}$	$f_i d_i$
20-30	10	25	-2	-20
30-40	6	35	-1	-6
40-50	8	45	0	0
50-60	12	55	1	12
60-70	5	65	2	10
70-80	9	75	3	27
	$\sum f_i = 50$			$\sum f_i d_i = 50$

Here,

a=45

and

h=10

\therefore \;\; \;\text{ Mean }\;=a+\frac{\sum f_i d_i}{\sum f_i} \times h

\;=45+\frac{23}{50} \times 10

\;=45+4.6=49.6

Go to Question:

Prev Question

Next Question