# hw3 - ISE 225 Engineering Statistics I Fall Semester 2010...

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ISE 225 Engineering Statistics I Homework #3 Fall Semester 2010 Due: Wednesday, September 15 1. Complete the following exercises from Hines, Montgomery, Goldsman, and Borror: 10-40 The life in hours of a 75-W light bulb is known to be approximately normally distributed, with a standard deviation of σ = 25 hours. A random sample of 20 bulbs has a mean life of 1014 x = hours. a) Construct a 95% two-sided confidence interval on the mean life. b) Construct a 95% lower-confidence interval on the mean life. 10-42 Suppose that in Exercise 10-40 we wanted to be 95% confident that the error in estimating the mean life is less than 5 hours. What sample size should be used? 11-2 part a) only, evaluate the test by using a critical point The yield of a chemical process is being studied. The variance of the yield is known from previous experience with this process to be 5 (units of σ 2 = percentage 2 ). The past five days of plant operation have resulted in yields (in percentages): 91.6, 88.75, 90.8, 89.95, 91.3. a)
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