The lifetime of a certain brand of electric light bulb is known to have a standard deviation of
51
hours. Suppose that a random sample of
150
bulbs of this brand has a mean lifetime of
481
hours. Find a
90%
confidence interval for the true mean lifetime of all light bulbs of this brand. Then complete the table below.
Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place. (If necessary, consult a list of formulas.)

The lower limit of the 90% confidence interval is 474.2 Rounded to one decimal place.
The upper limit of the 90% confidence interval is 487.8 Rounded to one decimal place.
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