Question

The following table gives the frequency distribution of trees planted by different Housing Societies in a particular locality:

No. of Trees	No. of Housing Societies
10-15	2
15-20	7
20-25	9
25-30	8
30-35	6
35-40	4

Find the mean number of trees planted by Housing Societies by using ‘Assumed Means Method’

Answer 1

By Assumed Mean Method 

No. of trees	Class mark                 xi	di=xi-A	No of housing              societies(fi)	fidi
10-15	12.5	-10	2	-20
15-20	17.5	-5	7	-35
20-25	`22.5toA`	0	9	0
25-30	27.5	5	8	40
30-35	32.5	10	6	60
35-40	37.5	15	4	60
Total	-	-	` sumf_i=36`	`sumf_id_i=105`

`bar d=(sumf_id_i)/(sumf_i)=105/36=2.916`

 Mean = `bar x=A+bard` = 22.5 + 2.916 = 25.42

Therefore the mean number of trees planted by Housing Societies is 25.42.