Question

The marks obtained out of 50, by 102 students in a Physics test are given in the frequency table below:

Marks(x)	15	20	22	24	25	30	33	38	45
Frequency (f)	5	8	11	20	23	18	13	3	1

Find the average number of marks.

Answer 1

Let the assumed mean (A) = 25

Marks (x1)	Frequency (f1)	u1= x1 - A x1 - 25	f1u1
15	5	-10	-50
20	8	-5	-40
22	11	-3	-33
24	20	-1	-20
25	23	0	0
30	18	5	90
33	13	8	104
38	3	13	39
45	1	20	20
	N = 102		`sumf_1"u"_1=110`

Average number of marks `=A + (sumf_1"u"_1)/N`

`=25+110/102`

`=(2550+110)/102`

`=2660/102`

= 26.08(Approx)