# Hypothesis Test Regarding a Population Mean Change

Please show all steps.

The mean lifetime of electric light blubs produced by a company has in the past been 1120 hours with a standard deviation of 125 hours. A sample of 8 electric bulbs recently chosen from a supply of newly produced bulbs showed a mean lifetime of 1070 hours. Test the hypothesis that the mean lifetime of the bulbs has not changed, using a level of significance of (a) 0.05 and (b) 0.01

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#### Solution Summary

This solution tests the null hypothesis that the mean life of bulbs equals a given value vs. the alternative that the mean differs from that value. All formulas and calculation details are provided along with explanations of each step of this step by step process.

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