The compressive strength of concrete is being tested by a civil engineer. He tests 12 specimens and

Question:

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

(a) Is there evidence to support the assumption that compressive strength is normally distributed? Does this data set support your point of view? 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.