Concept explainers
Nonpoint source loads are chemical masses that travel to the main stem of a river and its tributaries in flows that are distributed over relatively long stream reaches, in contrast to those that enter at well-defined and regulated points. The article “Assessing Uncertainty in Mass Balance Calculation of River Nonpoint Source Loads” (J. of Envir. Engr., 2008: 247–258) suggested that for a certain time period and location, X 5 nonpoint source load of total dissolved solids could be modeled with a lognormal distribution having
a. What are the mean value and standard deviation of ln(X)?
b. What is the probability that X is at most 15,000 kg/day/km?
c. What is the probability that X exceeds its mean value, and why is this probability not .5?
d. Is 17,000 the 95th percentile of the distribution?
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Chapter 4 Solutions
Probability and Statistics for Engineering and the Sciences
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- The article “Differences in Susceptibilities of Different Cell Lines to Bilirubin Damage” (K. Ngai, C. Yeung, and C. Leung, Journal of Paediatric Child Health, 2000:36–45) reports an investigation into the toxicity of bilirubin on several cell lines. Ten sets of human liver cells and 10 sets of mouse fibroblast cells were placed into solutions of bilirubin in albumin with a 1.4 bilirubin/albumin molar ratio for 24 hours. In the 10 sets of human liver cells, the average percentage of cells surviving was 53.9 with a standard deviation of 10.7. In the 10 sets of mouse fibroblast cells, the average percentage of cells surviving was 73.1 with a standard deviation of 9.1. Find a 98% confidence interval for the difference in survival percentages between the two cell lines.arrow_forwardThe article “Structural Performance of Rounded Dovetail Connections Under Different Loading Conditions” (T. Tannert, H. Prion, and F. Lam, Can J Civ Eng, 2007:1600–1605) describes a study of the deformation properties of dovetail joints. In one experiment, 10 rounded dovetail connections and 10 double rounded dovetail connections were loaded until failure. The rounded connections had an average load at failure of 8.27 kN with a standard deviation of 0.62 kN. The double-rounded connections had an average load at failure of 6.11 kN with a standard deviation of 1.31 kN. Can you conclude that the mean load at failure is greater for rounded connections than for double-rounded connections?arrow_forwardResearchers interested in lead exposure due to car exhaust sampled the blood of 52 police officers subjected to constant inhalation of automobile exhaust fumes while working traffic enforcement in a primarily urban environment. The blood samples of these officers had an average lead concentration of 124.32 µg/l and an SD of 37.74 µg/l; a previous study of individuals from a nearby suburb, with no history of exposure, found an average blood level concentration of 35 µg/l. Write down the hypotheses that would be appropriate for testing if the police officers appear to have been exposed to a higher concentration of lead. Explicitly state and check all conditions necessary for inference on these data. Test the hypothesis that the downtown police officers have a higher lead exposure than the group in the previous study. Interpret your results in context. Based on your preceding result, without performing a calculation, would a 99% confidence interval for the average blood concentration…arrow_forward
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