STATISTICS B2

In French 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	6	7	11	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 64.5 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	-50	4	58	-200
20-29	24.5	-40	5	122.5	-200
30-39	34.5	-30	6	207	-180
40-49	44.5	-20	7	311.5	-140
50-59	54.5	-10	11	599.5	-110
60-69	64.5	0	8	516	0
70-79	74.5	10	6	447	60
80-89	84.5	20	3	223.5	60
			∑f = 50	∑fx = 2458	∑fd = -710

Mean = A +  ∑fd

                       ∑f

Mean = 64.5 +  -710

                              50

Mean = 64.5 +  (-14.2)

                    

Mean = 50.3

         

Hence Mean =  50.3