Following table gives age distribution of people sufering from 'Asthma due to air pollution in certain city. Find mean age of persons suffering from 'Asthma' by 'Direct Method'.

2. Following table gives age distribution of people suffering from 'Asthama' due to air pollution in certain city.

Age in years	7-11	11-15	15-19	19-23	23-27	27-31	31-35	35-39
No. of people	5	9	13	21	16	15	12	9

Find mean age of person suffering from 'Asthama' by 'Direct Method'.

Sol. Class width ($h$) = 4

Age in years	Class Mark ($x_i$)	No. of people ($f_i$)	$f_ix_i$
7 - 11	9	5	45
11 - 15	13	9	117
15 - 19	17	13	221
19 - 23	21	21	441
23 - 27	25	16	400
27 - 31	29	15	435
31 - 35	33	12	396
35 - 39	37	9	333
Total		100	2388

$$ \text{Mean} = \frac{\sum f_ix_i}{\sum f_i} $$

$$ \therefore \text{Mean} = \frac{2388}{100} $$

$$ \therefore \text{Mean} = 23.88 \text{ years.} $$