The lifetime of a certain brand of electric light bulb is known to have a standard deviation of  50  hours. Suppose that a random sample of  90  bulbs of this brand has a mean lifetime of  488  hours. Find a  95%  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.)

MATLAB: An Introduction with Applications
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The lifetime of a certain brand of electric light bulb is known to have a standard deviation of 

50

 hours. Suppose that a random sample of 

90

 bulbs of this brand has a mean lifetime of 

488

 hours. Find a 

95%

 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.)

 

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