Question

Calculate the mean of the scores of 20 students in a mathematics test:

Marks	10 – 20	20 – 30	30 – 40	40 – 50	50 – 60
Number of students	2	4	7	6	1

Answer 1

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

Marks	Class marks `(bb(x_i))`	Frequency `(bb(f_i))`	`bb(f_ix_i)`
10 – 20	15	2	30
20 – 30	25	4	100
30 – 40	35	7	245
40 – 50	45	6	270
50 – 60	55	1	55
		`sumf_i = 20`	`sumf_ix_i = 700`

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

= `700/20`

= 35

Hence, the mean of scores of 20 students in mathematics test is 35.