The quality control manager at a light bulb factory needs to estimate the mean life of a large shipment of light bulbs. The standard deviation is 108 hours. A random sample of 81 light bulbs indicated a sample mean life of 340 hours. Complete parts​ (a) through​ (b) below.   a. Construct a 95​% confidence interval estimate for the population mean life of light bulbs in this shipment. The 95​% confidence interval estimate is from a lower limit of ______ hours to an upper limit of _____ hours.   b. Do you think that the manufacturer has the right to state that the lightbulbs have a mean life of 390 ​hours? Explain.

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