Statistics for Engineers and Scientists
4th Edition
ISBN: 9780073401331
Author: William Navidi Prof.
Publisher: McGraw-Hill Education
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Textbook Question
Chapter 5.4, Problem 12E
Refer to Exercise 11. Ten more welds will be made in order to increase the precision of the confidence interval. Which would increase the precision the most, cooling all 10 welds at the rate of 10°C/s, cooling all 10 welds at the rate of 30°C/s, or cooling 5 welds at 10°C/s and 5 at 30°C/s? Explain.
11. In a study of the effect of cooling rate on the hardness of welded joints, 50 welds cooled at a rate of 10°C/s had an average Rockwell (B) hardness of 91.1 and a standard deviation of 6.23, and 40 welds cooled at a rate of 30°C/s had an average hardness of 90.7 and a standard deviation of 4.34.
- a. Find a 95% confidence interval for the difference in hardness between welds cooled at the different rates.
- b. Someone says that the cooling rate has no effect on the hardness. Do these data contradict this claim? Explain.
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Chapter 5 Solutions
Statistics for Engineers and Scientists
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