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QUESTION 2: A researcher investigates the compressive strength of concrete when mixed with fly ash (a mixture of silica, alumina, iron, magnesium oxide, and other ingredients). The compressive strength for nine samples in dry conditions are as follows (in megapascals), note that the sample standard deviation was calculated to be (S= = 70.9): (4 points) 40.2 30.4 28.9 30.5 22.4 25.8 18.4 14.2 15.3 40+ 2 + 30. 4 + 28.9430.5 +22-4 +25. a. Find the sample mean compressive strength. = b. Find a 99% lower one-sided confidence interval on mean compressive strength. 125 c. Find a 95% two-sided confidence interval on mean compressive strength