Question

Find the mean deviation about the mean for the following data.

Marks obtained	10-20	20-30	30-40	40-50	50-60	60-70	70-80
Number of students	2	3	8	14	8	3	2

Answer 1

Marks obtained	Number of students fi	Midpoints Xi	fi xi	|xi - x|	fi|xi - x|
10-20	2	12	30	30	60
20-30	3	25	75	20	60
30-40	8	35	280	10	80
40-50	14	45	330	0	0
50-60	8	55	440	10	80
60-70	3	65	195	20	60
70-80	2	75	150	30	60
	N = 40 = ∑f		1800		∑f|x1 - x|2 = 400

Bar x = (∑f_ix_i)/N = 1800/40 = 45

MD (x) = 10.