Question: Question 11

The quality –control manager at a light-bulb factory needs to determine whether the mean life of a large shipment of light-bulbs is equal to the specified value of 375 hours. The process standard deviation is known to be 100 hours.

A random sample of 64 light-bulbs indicates a sample mean life of 350 hours.

a. Conduct a significance test at 5 % level to determine whether there is evidence that the mean life is different from 375 hours.

b. Set up a 95% confidence intervals estimate of the population mean life of the light-bulbs.