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lifetimes of two of its...

A light bulb manufacturer wants to compare the mean lifetimes of two of its light bulbs, model A and model B. Independent random samples of the two models were taken. Analysis of 13 bulbs of model A showed a mean lifetime of 1235 hours and a standard deviation of 81 hours. Analysis of 11 bulbs of model B showed a mean lifetime of 1372 hours and a standard deviation of 117 hours. Assume that the populations of lifetimes for each model are normally distributed and that the variances of these populations are equal. Construct a 95% confidence interval for the difference −μ1μ2 between the mean lifetime μ1 of model A bulbs and the mean lifetime μ2 of model B bulbs. Then complete the table below.

Carry your intermediate computations to at least three decimal places. Round your responses to at least two decimal places. (If necessary, consult a list of formulas.)What is the lower limit of the 95% confidence interval?

What is the upper limit of the 95% confidence interval?

Carry your intermediate computations to at least three decimal places. Round your responses to at least two decimal places. (If necessary, consult a list of formulas.)What is the lower limit of the 95% confidence interval?

What is the upper limit of the 95% confidence interval?

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