In a sample of 80 light bulbs, the mean lifetime was 1217 hours with a standard deviation of 52 hours.
a. Find a 95% confidence interval for the mean lifetime of this type of light bulb.
b. Find a 98% confidence interval for the mean lifetime of this type of light bulb.
c. An engineer claims that the mean lifetime is between 1208 and 1226 hours. With what level of confidence can this statement be made?
d. How many light bulbs must be sampled so that a 95% confidence interval will specify the mean lifetime to within ±8 hours?
e. How many light bulbs must be sampled so that a 98% confidence interval will specify the mean lifetime to within ±8 hours?
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