Q7 of 25 Page 332

To find out the concentration of 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:


Find the mean concentration of in the air.

Let’s find mean of the data using direct method as data given have smaller values.

First, construct a table for ease of calculation.



Mean is given by



⇒ Mean = 2.96/30


⇒ Mean = 0.0987


Or approximately, mean = 0.099


Thus, mean concentration of SO2 in the air is 0.099 ppm.


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