Periodically, the county Water Department tests the drinking water of homeowners

Question

Periodically, the county Water Department tests the drinking water of homeowners for contminants such as lead and copper. The lead and copper levels in water specimens collected in 1998 for a sample or 10 residents of a subdevelopement of the county are shown below. Construct a 99% confidence interval for the mean lead level in water specimans of the subdevelopment. 1.0878 lessthanorequalto mu lessthanorequalto 4.0922 Construct a 99% confidence interval for the mean copper level in water specimans of the subdevelopment. 0.165 lessthanorequalto mu lessthanorequalto 0.637

Explanation / Answer

as we knoe for 9 degree of freedom at 99% CI, t=3.2498

a) hence 99% CI for lead =mean +/- t*std error =0.6948 ; 4.4852

b)

99% CI for Cu =mean +/- t*std error =0.1033 ; 0.6987

S. no pb Cu 2.3 0.217 5.7 0.211 2.6 0.77 1.2 0.331 2.6 0.744 0.1 0.588 1.8 0.338 4.4 0.743 4.7 0.059 0.5 0.009 total 25.900 4.010 mean 2.590 0.401 std deviation(S) 1.844 0.290 std dev/(n)^(1/2) 0.583 0.092

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