Manufacturing, part 2.

The diameter of the copper wires must measure accurately to maintain quality and maximize profit. To ensure that error rates are estimated accurately, a quality controller wants to take a large enough sample to test the usable and accurate interval estimates of the diameters. He specifically wants the margin of error for the diameter to be not more than {0.02 mm.

a) Discuss how the quality controller may obtain a reasonable estimate of the standard deviation of error in the measured diameters.

b) Suppose the standard deviation of the diameters equals 0.1 mm. At 95% confidence, what sample size should be taken to ensure that the margin of error is not larger than

{0.01 mm?