Periodically, the Hillsborough County (Florida) Water Department tests the drinking water of homeowners for contaminants such as lead and copper. The lead and copper levels in water specimens collected for a sample of 10 residents of the Crystal Lakes Manors subdivision are shown below, followed by a Minitab printout analyzing the data.

a. Locate a 90% confidence interval for the mean lead level in water specimens from Crystal Lakes Manors on the printout.
b. Locate a 90% confidence interval for the mean copper level in water specimens from Crystal Lakes Manors on the printout.
c. Interpret the intervals, parts a and b, in the words of the problem.
d. Discuss the meaning of the phrase "90% confident."

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Lead (ug/L) Copper (mg/L) 508 279 320 .904 221 283 475 130 220 743 13.1 919 .657 3.0 1.32 4.09 4.45 Variable N Mean StDev SE Mean LEAD COPPER 10 О.4083 0.2495 0.0789 (0.2637,0.5529) 903 CI 10 2.89 3.92 .24 0.61, .16)