95% = mean ± 1.695 SEm
SEm = SD/√n
The Ledd Pipe Company has received a large shipment of pipes, and a quality control inspector wishes to
estimate the average diameter of these pipes. A random sample of 18 pipes produces an average diameter of
2.56 mm with a standard deviation of 0.05 mm. You may assume that the diameters of the pipes are normally
distributed.
(A) Give a 95% confidence interval for the average diameter of pipes in this shipment.
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