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 a certain area was 0.15 milligrams per liter (mg/L). A random sample of 10 precipitation dates in 2007 results in the following data table:
0.064, 0.088, 0.072, 0.239, 0.114, 0.184, 0.136, 0.214, 0.315, 0.106
a) Construct a 99% confidence interval about the sample mean concentration of calcium precipitation:
(____,____) (use ascending order, round to four decimal places)
b) Does the sample evidence suggest that calcium concentrations have changed since 1990?