1. Crop researchers plant 15 plots with a new variety of corn. The yields in bushels per acre are: 138.0 139.1 113.0 132.5 140.7 109.7 118.9 134.8 109.6 127.3 115.6 130.4 130.2 111.7 105.5 Assume thatbushels per acre. a) Find the 90% confidence interval for the mean yield for this variety of corn. b) Find the 95% confidence interval. c) Find the 99% confidence interval. d) How do the margins of error in (a), (b), and (c) change as the confidence level increases?

2. A newspaper ad for a manager trainee position contained the statement "Our manager trainees have a first-year earnings average of $20,000 to $24,000." Do you think that the ad is describing a confidence interval? Explain your answer.

3. Please show your thinking through your work: a) As sample size goes up, the width of the confidence interval gets. b) As sample size goes down, the width of the confidence interval gets. c) As confidence level goes up, the width of the confidence interval gets. d) As confidence level goes down, the width of the confidence interval gets.