A random sample of 27 items is drawn from a population whose standard deviation is unknown. The sample mean is Xbar = 940 and the sample standard deviation is s = 15. Use Appendix D to find the values of students's t.

(a) Construct an interval estimate of mean with 99% confidence. (Round your answers to 3 decimal places.)

The 99% confidence interval is from- To-

(b) Construct an interval estimate of mean with 99% confidence, assuming that s = 30. (Round your answers to 3 decimal places.)

The 99% confidence interval is from- To-

(c) Construct an interval estimate of mean with 99% confidence, assuming that s= 60. (Round your answers to 3 decimal places)

The 99% confidence interval is from- To-