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Testing the Manufacturing Quality Process

A manufacturer receives an order for light bulbs. The order requires the bulbs have a mean life span of 750 hours. The manufacturer selects a random sample of 25 light bulbs and find they have a mean life of 745 hours with a standard deviation of 15 hours. Test to see if the manufacturer is making acceptable light bulbs. Assume the data are normally distributed. Show your curve. a=0.05

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Denote by mu the mean life span. Then we would like to test

H0: mu=750
Ha: mu is NOT equal to 750.

Now we use z-test. As the sample mean ...

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