STATISTICS B5

In Mathematics 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	6	9	10	13	8	7	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 44.5 as our assumed mean (A). Take away the assumed mean from each class mark.

Class interval	Class mark (x)	d=x-A	Frequency(f)	fd
10-19	14.5	-30	4	-120
20-29	24.5	-20	6	-120
30-39	34.5	-10	9	-90
40-49	44.5	0	10	0
50-59	54.5	10	13	130
60-69	64.5	20	8	160
70-79	74.5	30	7	210
80-89	84.5	40	3	120
			∑f = 60	∑fd = 290

Mean = A +  ∑fd

                      ∑f

Mean = 44.5 +  290

                          60

Mean = 44.5 +  (4.83)

                    

Mean = 49.33   (to 2d.p)

         

Hence Mean =  49.33