Find the mean of the following frequency distribution:

Class 1-3 3-5 5-7 7-9

Frequency 9 22 27 18

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Solution

We have the following table:

Class

Mid value $(x_{i})$

Frequency $(f_{i})$

$f_{i} x_{i}$

1-3

2

9

18

3-5

4

22

88

5-7

6

27

162

7-9

8

18

144

$\sum f_{i} = 76$

$\sum f_{i} x_{i} = 412$

$∴ Mean, \bar{x} = \frac{\sum f_{i} x_{i}}{\sum f_{i}} = \frac{412}{76} = 5.42$

Suggest Corrections

Size of Items	3−4	4−5	5−6	6−7	7−8	8−9	9−10
Frequency	3	7	22	60	85	32	9

Variable (x_i)	10	30	50	70	89
Frequency (f_i)	7	8	10	15	10

Class	0 − 20	20 − 40	40 − 60	60 − 80	80 − 100	100 – 120	120 – 140
Frequency	6	8	10	12	6	5	3

Class	1−3	3−5	5−7	7−9
Frequency	12	22	27	19