In: Statistics and Probability
Calculate true standard deviation of the diameter of a large batch of tires to a confidence level of 99% if the measured standard deviation in the diameter for a sample of 30 tires is 0.0795 cm.
Solution :
Given that,
c = 99% = 0.99
s = 0.0795
n = 30
d.f. = n - 1 = 30 - 1 = 29
= 1 - 0.99 = 0.01
/ 2 = 0.005
1 - (
/ 2) = 0.995
Now , using chi square table ,
=
0.025,29 = 52.335
=
0.975,26
= 13.121
The 99% confidence interval for
is,
0.0795 [(30
- 1 ) / 52.335] <
< 0.0795
[(30
- 1 ) / 13.121]
0.059 <
< 0.118
The 99% confidence interval for
is ( 0.059 , 0.118 )