ifetime of a certain brand of electric light bulb is known to have a standard deviation of
5
5
hours. Suppose that a random sample of
6
0
bulbs of this brand has a mean lifetime of
4
9
4
hours. Find a
9
5
%
confidence interval for the true mean lifetime of all light bulbs of this brand. Then give its lower limit and upper limit
.
Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.
(
If necessary, consult a list of formulas.
)
Lower limit:
Upper limit
