Consider the following distribution of SO2 concentration in the air(in ppm = parts per million) in 30 localities. We wish to find the mean SO2 concentration using step assumed mean method.Fill the following table. Determine the assumed mean(a) and proceed.
Class IntervalFrequency(fi)Class mark(xi)di=xi−a0−1004050−200D......0.00−0.0440.02−0.080.04−0.0890.06A.........0.08−0.1290.10B........0.12−0.1620.140.040.16−0.2040.18C........0.20−0.2420.220.12Total∑fi=30
The value of A, B and C respectively are:
0.04, 0 and 0.08
The 4th column in table shown in question is a table of values of ‘d’.
dj = value of ‘d’ for ith class mark-row.
xi = ith class mark
a = assumed mean value
Applying given formula for 1st class interval(0-0.04),
-0.08 = 0.02 – a
a = 0.1
Thus P = 0.1
Applying given formula for 2nd class interval(0.04-0.08)
A = 0.06 – 0.1
A = -0.04
Similarly for 3rd and 5th classes d values are-
B = 0
C = 0.04