Question

The following table gives the marks scored by a set of students in an examination. Calculate the mean of the distribution by using the short cut method.

Marks	Number of Students (f)
0 – 10	3
10 – 20	8
20 – 30	14
30 – 40	9
40 – 50	4
50 – 60	2

Answer 1

Let assumed mean A = 25

C.I. marks	xi	fi	di = xi – A	fidi
0 – 10	5	3	– 20	– 60
10 – 20	15	8	– 10	– 80
20 – 30	25 = A	14	0	0
30 – 40	35	9	10	90
40 – 50	45	4	20	80
50 – 60	55	2	30	60
		n = 40		`sumf_i d_i` = 90

Mean = `A + (sumf_i d_i)/n`

= `25 + 90/40`

= 25 + 2.25

= 27.25 marks