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 of 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. Lessthanorequalto mu lessthanorequalto Construct a 99% confidence interval for the mean copper level in water specimans of the subdevelopment. Lessthanorequalto mu lessthanorequalto

Explanation / Answer

a)

degree of freedom =n-1=9

for 9 df and 99% CI, t=3.2498

hence confidence interval =mean +/- t*std error =1.711 <mu<5.449

b)

degree of freedom =n-1=9

for 9 df and 99% CI, t=3.2498

hence confidence interval =mean +/- t*std error =0.216 <mu<0.860

lead 5.100 2.100 3.700 2.200 4.800 5.700 4.900 5.000 2.100 0.200 mean(X) 3.580 std deviation(S) 1.819 std error =S/(n)1/2 0.575

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