Page 149 - Statistics for Environmental Engineers

L1592_Frame_C16 Page 146 Tuesday, December 18, 2001 1:51 PM

easily be 90%. The data, in percentages, are 92, 60, 77, 92, 100, 90, 91, 82, 75, 50. Who is
correct and why?
16.2 Fermentation. Gas produced from a biological fermentation is offered for sale with the
assurance that the average methane content is 72%. A random sample of n = 7 gas specimens
gave methane contents (as %) of 64, 65, 75, 67, 65, 74, and 75. (a) Conduct hypothesis tests
at significance levels of 0.10, 0.05, and 0.01 to determine whether it is fair to claim an average
of 72%. (b) Calculate 90%, 95%, and 99% confidence intervals to evaluate the claim of an
average of 72%.
16.3 TOC Standards. A laboratory quality assurance protocol calls for standard solutions having
50 mg/L TOC to be randomly inserted into the work stream. Analysts are blind to these
standards. Estimate the bias and precision of the 16 most recent observations on such stan-
dards. Is the TOC measurement process in control?

50.3 51.2 50.5 50.2 49.9 50.2 50.3 50.5 49.3 50.0 50.4 50.1 51.0 49.8 50.7 50.6

16.4 Discharge Permit. The discharge permit for an industry requires the monthly average COD
concentration to be less than 50 mg/L. The industry wants this to be interpreted as “50 mg/L
falls within the confidence interval of the mean, which will be estimated from 20 observations
per month.” For the following 20 observations, would the industry be in compliance according
to this interpretation of the standard?

57 60 49 50 51 60 49 53 49 56 64 60 49 52 69 40 44 38 53 66

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