A random sample of 23 items is drawn from a population whose standard deviation Is unknown. The sample mean is x = 840 and the sample standard deviation Is s = 15. Use Appendix D to find the values of Student's t 5 (a) Construct an Interval estimate of / with 98% confidence. (Round your answers to 3 decimal places.) points The 98% confidence Interval is from to eBook Ask (b) Construct an Interval estimate of / with 98% confidence, assuming that s = 30. (Round your answers to 3 decimal places.) Print The 98% confidence interval is from to n References (c) Construct an interval estimate of / with 98% confidence, assuming that s = 60. (Round your answers to 3 decimal places.) The 98% confidence interval is from to (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