# Statistics

posted by Carolyn

A quality control inspector wants to estimate the mean inside diameter of the washers produced by a
certain machine. A preliminary sample indicates that the inside diameters have a standard deviation
of 0.30 millimeters. What sample size does he need to estimate the mean to within an error of E = 0.02
millimeters with 90% confidence?

1. PsyDAG

90% = mean ± 1.645 SEm

SEm = SD/√n

.02 = 1.645 SEm

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