STATISTICS B3

In Biology test the following marks were recorded.

marks	10-19	20-29	30-39	40-49	50-59	60-69	70-79	80-89
No. of students	4	5	8	9	12	8	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	4	58	-80
20-29	24.5	-10	5	122.5	-50
30-39	34.5	0	8	276	0
40-49	44.5	10	9	400.5	90
50-59	54.5	20	12	654	240
60-69	64.5	30	8	516	240
70-79	74.5	40	6	447	240
80-89	84.5	50	3	223.5	150
			∑f = 55	∑fx = 2697.5	∑fd = -830

Mean = A +  ∑fd

                       ∑f

Mean = 34.5 +  -830

                              55

Mean = 34.5 +  (-15.091)

                    

Mean = 19.409

         

Hence Mean =  19.409