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# Statistics

#### Question 7:

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 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

Find the mean concentration of SO2 in the air.

To find the class marks for each interval, the following relation is used.

Class size of this data = 0.04

Taking 0.14 as assumed mean (a), di, ui, fiui are calculated as follows.

 Concentration of SO2 (in ppm) Frequency fi Class mark xi di = xi − 0.14 …

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