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CEE 110 PS5 11


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UNIVERSITY OF CALIFORNIA, LOS ANGELES Civil and Environmental Engineering Department CEE 110 Introduction to Probability and Statistics for Engineers Spring Quarter 2011 MW 12-2 PM Franz 1178 Prof. K. D. Stolzenbach 5732J Boelter Hall, 206-7624 [email protected] Problem Set 5 (Due Wednesday May 11, 2011) _____________________________________________________________________________ 1. (problem 8.14 in text) The life in hours of a 75-watt light bulb is known to be normally distributed with σ = 25 hours. A random sample of 20 bulbs has a mean life of x = 1014 hours. (a) Construct a 95% two-sided confidence interval on the mean life. (b) Construct a 95% lower-confidence bound on the mean life. Compare the lower bound of this confidence interval with the one in part (a). [1003, 1025; 1005] 2. (problem 8.16 in text) Suppose that in Problem 1 we wanted the error in estimating the mean life from the two- sided confidence interval to be five hours at 95% confidence. What sample size should be used? [97] 3. (problem 8.28 in text) An Izod impact test was performed on 20 specimens of PVC pipe. The sample mean is x = 1.25 and the sample standard deviation is s = 0.25. Find a 99% lower confidence bound on
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