UNIVERSITY OF CALIFORNIA, LOS ANGELES
Civil and Environmental Engineering Department
CEE 110 Introduction to Probability and Statistics for Engineers
Spring Quarter 2011
MW 122 PM
Franz 1178
Prof. K. D. Stolzenbach
5732J Boelter Hall, 2067624
[email protected]
Problem Set 5
(Due Wednesday May 11, 2011)
_____________________________________________________________________________
1. (problem 8.14 in text)
The life in hours of a 75watt 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% twosided confidence interval on the mean life.
(b)
Construct a 95% lowerconfidence 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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 Spring '11
 Yukov
 Normal Distribution, Environmental Engineering, Boelter Hall, twosided confidence interval, FRANZ 1178, Journal of Composite Materials

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