Chapter 15 - Statistics

Example 5. Calculate the arithmetic mean of the following frequency distribution:

Class Interval	0-30	30-60	60-90	90-120	120-150	150-180
Frequency	12	21	34	52	20	11

Solution:-

Class interval	Frequency	xi	di = xi - 105	fi di
0-30	12	15	-90
30-60	21	45	-60
60-90	34	75	-30
90-120	52	105 = a	0	-0
120-150	20	135	30
150-180	11	165	60

Here, a = 105

Arithmetic mean =