The compressive strength of concrete is being tested by a civil engineer who tests 12 specimens and obtains the following data:

(a) Check the assumption that compressive strength is normally distributed. Include a graphical display in your answer.

(b) Construct a 95% two-sided confidence interval on the mean strength.

(c) Construct a 95% lower confidence bound on the mean strength. Compare this bound with the lower bound of the two-sided confidence interval and discuss why they are different.

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