At a local plant batteries are being produced with a life ex

At a local plant, batteries are being produced with a life expectancy that has a variance of 5.6 months squared. Suppose the mean life expectancy in a sample of 64 batteries is 12.35 months.

a. Find the 90% confidence interval estimate of the mean life expectancy for all batteries produced at this plant.

b. What would the 90% confidence interval estimate be if the sample mean had come from a sample of 100 batteries?