Given below is the concentration of SO2 in air (in ppm = parts per million) in 30 localities:
SO2 concentration (in ppm)Number of localities0.00−0.0440.04−0.0890.08−0.1290.12−0.1620.16−0.2040.20−0.242
Find the mean of SO2 concentration using assumed - mean method.
0.099
Let assumed mean, i.e., a=0.10. Now let us form the table and tabulate the mean of SO2 concentration:
Class intervalFrequency(fi)Class mark(xi)di=xi−afidi0.00−0.0440.02−0.08−0.320.04−0.0890.06−0.04−0.360.08−0.1290.100.000.000.12−0.1620.140.040.080.16−0.2040.180.080.320.20−0.2420.220.120.24Total∑fi=30∑fidi=−0.04
Mean=(x)=a+∑fidi∑fi=0.10+−0.0430=0.099
So, the mean of SO2 concentration = 0.099