STATISTICS B9

In Geography test the following marks were recorded.

marks	10-14	15-19	20-24	25-29	30-34	35-39	40-44	45-49
No. of students	3	6	7	9	12	8	6	4

Calculate the mean.

Solution

In this question we are going to apply the method of assumed mean.

Here you are required to produce the frequency distribution table.

Let us take 37 as our assumed mean (A). Take away the assumed mean from each class mark.

Class interval	Class mark (x)	d=x-A	Frequency(f)	fd
10-14	12	-25	3	-75
15-19	17	-20	6	-120
20-24	22	-15	7	-105
25-29	27	-10	9	-90
30-34	32	-5	12	-60
35-39	37	0	8	0
40-44	42	5	6	30
45-49	47	10	4	40
			∑f = 55	∑fd = -380

Mean = A +  ∑fd

                      ∑f

Mean = 37 +  (-380)

                          55

Mean = 37 +  (-6.91)

                    

Mean = 30.09  (to 2d.p)

          

Hence Mean =  30.09