Two brands of tyres are to be compared for their mean life. The following data are available
Life (thousand km.)
10-15
15-20
20-25
25 - 30
30 - 35
35-40
No. of tyres of brand A
4
7
10
5
3 1
No. of tyres of brand B
5
8
15
9
6
2.
On the basis of mean, which brand of tyres is better?
Answers
Given : Two brands of tyres are to be compared for their mean life.
To Find : On the basis of mean, which brand of tyres is better?
Solution:
brand A
Life (thousand km.) Mean life A=(Mean - 22.5)/10 f A.f
10-15 12.5 -2 4 -8
15-20 17.5 -1 7 -7
20-25 22.5 0 10 0
25 - 30 27.5 1 5 5
30 - 35 32.5 2 3 6
35-40 37.5 3 3 9
30 5
Mean = 22.5 + 5 * 10/30
= 22.5 + 1.67
= 24.167
brand B
Life (thousand km.) Mean life A=(Mean - 22.5)/10 f A.f
10-15 12.5 -2 5 -10
15-20 17.5 -1 8 -8
20-25 22.5 0 15 0
25 - 30 27.5 1 9 9
30 - 35 32.5 2 6 12
35-40 37.5 3 2 6
45 9
Mean = 22.5 + 9 * 10/45
= 22.5 + 2
= 24.5
24.5 > 24.167
On the basis of mean brand of tyres B is better
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