SOLUTION: The lifetime of a certain brand of battery is known to have a standard deviation of 11.5 hours. Suppose that a random sample of 80 such batteries has a mean lifetime of 43.9 hours.

Question 1159791: The lifetime of a certain brand of battery is known to have a standard deviation of 11.5 hours. Suppose that a random sample of 80 such batteries has a mean lifetime of 43.9 hours. Based on this sample, find a 99% confidence interval for the true mean lifetime of all batteries of this brand.
Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.
What is the lower limit of the 99% confidence interval?

What is the upper limit of the 99% confidence interval?
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
half-interval is z(0.995)*sigma/sqrt(n)
=2.576*11.5/sqrt(80)
=3.31
99% CI is mean+/- margin of error
(40.6, 47.2) hours
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