Question 7

To find out the concentration of $\text{SO}_2$ 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:

$$\begin{array}{|c|c|}

\hline
\text{Concentration of } \text{SO}_2 \text{ (in ppm)} & \text{Frequency} \\
\hline
0.00 - 0.04 & 4 \\
0.04 - 0.08 & 9 \\
0.08 - 0.12 & 9 \\
0.12 - 0.16 & 2 \\
0.16 - 0.20 & 4 \\
0.20 - 0.24 & 2 \\
\hline
\end{array}$$

Find the mean concentration of $\text{SO}_2$ in the air.