A random sample of 27 items is drawn from a population whose standard deviation is unknown. The sample mean is = 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 μ with 99% confidence.
(b) Construct an interval estimate of μ with 99% confidence, assuming that s = 30.
(c) Construct an interval estimate of μ with 99% confidence, assuming that s = 60.
(d) Describe how the confidence interval changes as s increases.
The interval stays the same as s increases.
The interval gets wider as s increases.
The interval gets narrower as s increases.