statitics
posted by jamie on .
a light bulb manufacture gaurentees that the mean life of a certain type of bulb is at least 875 hours. A random sample of 40 light bulbs has a mean life of 863 hours with a standard deviation of 50. a=0.04

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Work: A random sample of 100 light bulbs has a mean lifetime of 3000 hours. Assume that the population standard deviation of the lifetime is 500 hours. Construct a 95% confidence interval estimate of the mean lifetime

What
percentage of light bulb fail to satisfy to guarantee