STATISTICS A7

In Biology test the following marks were recorded.

marks	10-19	20-29	30-39	40-49	50-59
No. of students	2	4	5	6	3

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 34.5 as our assumed mean(A). Take away the assumed mean from each class mark.

Class interval	Class mark (x)	d=x-A	Frequency(f)	fx	fd
10-19	14.5	-20	2	29	-40
20-29	24.5	-10	4	98	-40
30-39	34.5	0	5	172.5	0
40-49	44.5	10	6	267	60
50-59	54.5	20	3	163.5	60
			∑f = 20	∑fx = 730	∑fd = 40

Mean = A +  ∑fd

                       ∑f

Mean = 34.5 +  40

                            20

Mean = 34.5 +  2

                           

         

Hence Mean =  36.5

Also you can prove your answer by using the normal formula of calculating mean, that is ∑fx/∑f and try to see if you get the same answer.