Question

Calculate the mean of the following data:

Class	4 – 7	8 – 11	12 – 15	16 – 19
Frequency	5	4	9	10

Answer 1

Since, given data is not continuous, so we subtract 0.5 from the lower limit and add 0.5 in the upper limit of each class.

Now, we first find the class mark x_i of each class and then proceed as follows.

Class	Class marks `(bb(x_i))`	Frequency  `(bb(f_i))`	`bb(f_ix_i)`
3.5 – 7.5	5.5	5	27.5
7.5 – 11.5	9.5	4	38
11.5 – 15.5	13.5	9	121.5
15.5 – 19.5	17.5	10	175
		`sumf_i = 28`	`sumf_ix_i = 362`

Therefore, mean `(barx) = (sumf_ix_i)/(sumf_i)`

= `362/28`

= 12.93

Hence, mean of the given data is 12.93.