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 $$ \text{Mean} = \frac{\sum f_ix_i}{\sum f_i} $$
$$ \therefore \text{Mean} = \frac{2388}{100} $$
$$ \therefore \text{Mean} = 23.88 \text{ years.} $$