a random sample of 12 items is drawn from a population whose standard deviation is unknown. the sample mean is x(line over top)=800 and the sample standard deviation is s=10. use Appendix D to find the values of students t.

A. Construct an interval estimate of U with a 95% confidence (round your answer 3 decimal places)

The 95% confidence interval is from _________ to _________

B construct an interval estimate of U with 95% confidence assuming that s=20 (round your answer 3 decimal places)

The 95% confidence interval is from ________ to __________

C. Construct an interval estimate of U with 95% confidence assuming that s=40

The 95% confidence interval is from ____ to _____________

Describe how the confidence interval changes as s increases

the iternal stays the same as s increases

the internal gets wider as s increases

The internal gets narrower as s increases