Question

Please answer neatly and correctly!

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 15 bulbs of model A showed a mean lifetime of 1350 hours and a standard deviation of 102 hours. Analysis of 14 bulbs of model B showed a mean lifetime of 1384 hours and a standard deviation of 91 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 u, -u, between the mean lifetime u, of model A bulbs and the mean lifetime u, 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? x o ?

Answer 1

The statistic software output for this problem is:

Two sample T summary confidence interval: Vi : Mean of Population 1 P2 : Mean of Population 2 H1 - H2 : Difference between two means (with pooled variances) 95% confidence interval results: Difference Sample Diff. Std. Err. DF L. Limit U. Limit 1 - H2 -34 35.994221 27 -107.85404 39.854041

The 95% confidence interval is :

Lower limit = -107.854

Upper limit = 39.854