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The life of a machine is normally distributed with a standard deviation of 35 hours. A...

The life of a machine is normally distributed with a standard deviation of 35 hours. A quality assurance officer takes a sample of 60 machines randomly from a batch containing 5000 machines. The average life of this sample is between 1385.45 and 1405.62 hours.

a) Find a 90% confidence interval to estimate the average life of machines in this lot.

Math   Statistics-And-Probability   
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Answer #1

Solution:

From given information,

Population standard deviation = 35

Sample size = n = 60

We have to find sample mean from given range.

Sample mean = = 1385.45 + 1405.62 / 2

Sample mean = = 1395.53

Hence 90% confidence interval is , ( 1388.098 , 1402.962 )

Done

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