Sec_8_solutions__10_29_04_ - CEE 304 Section#8 Example...

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1 CEE 304 Section #8 Example Problems (10-26-04) 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 high-strength 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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2 Hypothesis Testing Example ° Devore, Sec. 8.1, #11 The calibration of a scale is to be checked by weighing a 10-kg test specimen 25 times.
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