A random sample of 10 items is drawn from a population whose standard deviation is unknown. The sample mean is x-bar = 270 and the sample standard deviation is s = 20. Use Appendix D to find the values of Student's t.
a. Construct an interval estimate for with 95 percent confidence.
b. Repeat part a assuming that n = 20.
c. Repeat part a assuming that n = 40.
d. Describe how the confidence interval changes as n increases.