A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with 2

Question:

A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with σ2 = 1000(psi)2. A random sample of 12 specimens has a mean compressive strength of x = 3250 psi.
(a) Construct a 95% two-sided confidence interval on mean compressive strength.
(b) Construct a 99% two-sided confidence interval on mean compressive strength. Compare the width of this confidence interval with the width of the one found in
part (a).