Question

1. A plant distills liquid air to produce oxygen, nitrogen, and argon. The percentage of impurity in the oxygen is thought to be linearly related to the amount of impurities in the air as measured by the “pollution count” in part per million (ppm). A sample of plant operating data is shown below.

       Purity(%)                        93.3    92.0    92.4    91.7    94.0    94.6    93.6    93.1    93.2    92.9    92.2 91.3 90.1    91.6    91.9

       Pollution count (ppm)    1.10    1.45    1.36    1.59    1.08    0.75    1.20    0.99    0.83    1.22    1.47    1.81 2.03    1.75    1.68

1. Find the 95% confidence interval for the mean purity at 1.10 ppm, and also the 95% confidence interval for a single observation at 1.10 ppm (use software – in Statgraphics check Forecasts in Tables and Graphs).

Answer 1

	Purity(%)	Pollution count (ppm)
count	15	15
confidence interval 95.% lower	91.884	1.1468
confidence interval 95.% upper	93.170	1.5612
margin of error	0.643	0.2072
t(df = 14)	2.145	2.145