In a sample of 60 electric motors, the average efficiency (inpercent) was 85 and the standard deviation was 2.
a. Find a 95% confidence interval for the mean efficiency.
b. Find a 99.5% confidence interval for the mean efficiency.
c. What is the confidence level of the interval (84.63,85.37)?
d. How many motors must be sampled so that a 95% confidence interval specifies the mean to within±0.35?
e. How many motors must be sampled so that a 99.5% confidence interval specifies the mean to within ±0.35?
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