9.77 The Rockwell hardness measure of steel ingots is produced by pressing a diamond point into the...

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9.77 The Rockwell hardness measure of steel ingots is produced by pressing a diamond point into the steel and measuring the depth of penetration. A sample of 15 Rockwell hardness measurements on specimens of steel gave a sample mean of 65 and a sample variance of 90. Estimate the true mean hardness in a 95% confidence interval, assuming the measurements to come from a normal distribution.

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Probability And Statistics For Engineers

ISBN: 9781133006909

5th Edition

Authors: Richard L Scheaffer, Madhuri Mulekar, James T McClave, Cecie Starr

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