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)



Frequency



0.00 - 0.04


0.04 - 0.08


0.08 - 0.12


0.12 - 0.16


0.16 - 0.20


0.20 - 0.24



4


9


9


2


4


2



Find the mean concentration of SO2 in the air


The above given data can be represented in the form of table as below:


Class interval



fi



xi



fixi



0.00-0.04



4



0.02



0.08



0.04-0.08



9



0.06



0.54



0.08-0.12



9



0.10



0.90



0.12-0.16



2



0.14



0.28



0.16-0.20



4



0.18



0.72



0.20-0.24



2



0.22



0.44




∑fi = 30




∑fixi = 2.96



Mean can be calculated as follows:




= 0.099 ppm


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