A random sample of 27 items is drawn from a population whose standard deviation is unknown. The sample mean is x

= 940 and the sample standard deviation is s = 15. Use Appendix D to find the values of Student's t.

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

The 99% confidence interval is from to

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

The 99% confidence interval is from to

(d) Describe how the confidence interval changes as s increases.

multiple choice

• The interval stays the same as s increases.
• The interval gets wider as s increases.
• The interval gets narrower as s increases.