SOLUTION: 4. Weight of Containers Find the 90% confidence interval for the variance and standard deviation for the lifetime of disposable camera batteries if a sample of 16 disposable cam

Question 1173268: 4. Weight of Containers Find the 90% confidence
interval for the variance and standard deviation for the
lifetime of disposable camera batteries if a sample of
16 disposable camera batteries has a standard deviation
of 2.1 months. Assume the variable is normally
distributed. Do you feel that the lifetimes of the
batteries are relatively consistent?
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
this is a ChiSq with df=15
(n-1)s^2/CSq lower < sigma^2 < (n-1)s^2/ChiSq upper
from the table, using .05 for the first and 0.95 for the second
15*4.41/24.996 < sigma^2 < 15*4.41/7.261; the 4.41 is 2.1^2
2.65 < sigma ^2 < 9.11 which is the 90% CI for the variance
take the square root of everything to get the 90% CI of the sd
(1.63, 3.02) units months.
The last part of the question is opinion and has a good deal to do with the mean life, which isn't stated.
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