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Purchasing Manager Tests Lifetimes of Light Bulbs for LCD Projectors

A purchasing manager for a large university is investigating which brand of LCD projector to purchase to equip "smart" classrooms. Of major concern is the longevity of the light bulbs used in the projectors. The purchasing manager has narrowed down the choice of projector to two brands, Infocus and Proxima, and wishes to determine if there is any difference between the two brands in the mean lifetime of the bulbs used.

The purchasing manager obtained eight projectors of each brand for testing over the last several academic terms. The number of hours the bulbs lasted on each of the eight machines is given in the table.

Lifetimes of lightbulbs

infocus 957, 710 910 730 1002 955 934
proxima 1023 771 864 971 663 869 772 956

Assume that the two populations of lifetimes are normally distributed and that the population variances are equal. Can we conclude, at the level of significance, that there is a difference in the mean lifetime of the light bulbs in the two brands?
Perform a two-tailed test. Then fill in the table below.

Carry your intermediate computations to at least three decimal places and round your answers as specified in the table. (If necessary, consult a list of formulas).

Solution Summary

The solution provides an answer to the lifetimes of light bulbs.