(Q15). To find out the concentration of SO2 in the air (in parts per million, i.e., ppm), the data was collected for 30 localities in a certain city and is presented below:

Concentration of SO2 in ppm 0.00-0.04 0.04-0.08 0.08-0.12 0.12-0.16 0.16-0.20 0.20-0.24
Frequency 4 9 9 2 4 2

Find the mean concentration of SO2 in the air.

Solution :

Concentration of SO2 in ppm frequency(fi) Class Marks (xi) fixi
0.00-0.04 4 0.02
0.04-0.08 9 0.06
0.08-0.12 9 0.10
0.12-0.16 2 0.14
0.16-0.20 4 0.18
0.20-0.24 2 0.22
- ∑fi = 30 - ∑fixi =
x̄ =
∑fixi
∑fi
 =
30
 ≅