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Confidence interval and sample size needed


A company manufactures steel bolts that continuously feed an assembly line downstream. Historically, the thickness of these bolts follows a normal distribution with a standard deviation of 1.6 mm. A recent random sample of 10 observations yielded these values of thickness, in mm:

9.7 9.9 10.3 10.1 10.5
9.4 9.9 10.1 9.7 10.3

a.Construct a 95% confidence interval for the true mean thickness.
b.Find the number of observations, n, required to estimate the true mean thickness to within
±0.2 mm using a 95% confidence interval.


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