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# Hypothesis Test Regarding a Standard Deviation Irregularity

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The mean lifetime of electric light bulbs produced by a company has in the past been 1120 hours with a standard deviation of 125 hours. A sample of 20 bulbs revealed a standard deviation in the lifetimes of 150 hours. Would you conclude that this is unusual? Explain.

##### Solution Summary

This problem is a test of hypothesis comparing the variance (and standard deviation) of a new distribution with a known variance from another distribution. A step by step process is used, all formulas and calculations are shown and each step is explained.

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