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1
CEE 304
−
Section #8 Example Problems (102604)
Confidence Intervals for Small Samples:
1. An environmental engineer is studying the concentration of organics in a groundwater
source for a rural water supply. Twelve samples yielded a sample mean and variance of
24.3
µ
g/l and 81 (
µ
g/l)
2
, respectively.
a.) Construct a 99% confidence interval for the true mean concentration of organics in
this source of water assuming individual observations have a normal distribution.
b.) What is the probability the true mean value is contained in the particular interval you
just calculated?
2. The sample average ultimate tensile strength for a sample of 35 highstrength magnetic
alloy steel rings used in turbine generators was 152.3 ksi, while the sample standard
deviation was 4.8 ksi. Obtain a 99% confidence interval for the true average tensile
strength of such rings.
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Hypothesis Testing Example & Devore, Sec. 8.1, #11
The calibration of a scale is to be checked by weighing a 10kg test specimen 25 times.
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This note was uploaded on 02/02/2008 for the course CEE 3040 taught by Professor Stedinger during the Fall '08 term at Cornell University (Engineering School).
 Fall '08
 Stedinger

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