Calcium is essential to tree growth because it promotes the formation of wood and maintains cell walls. In 1990, the concentration of calcium in precipitation in Chautauqua, New York, was 0.11 milligram per liter (mg/L). A random sample of 10 precipitation dates in 2010 results in the following data:
(a) Because the sample size is small, we must verify that calcium concentrations are normally distributed and the sample does not have any outliers. The normal probability plot and boxplot are shown. Are the conditions for conducting the hypothesis test satisﬁed?
(b) Does the sample evidence suggest that calcium concentrations have changed since 1990? Use the α = 0.05 level of signiﬁcance.
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