1. The Excel file Mortgage Rates contains time‐series data on rates of three different mortgage instruments. Assuming that the data are stationary, construct a 95% confidence interval for the mean difference between the 30‐year and 15‐year fixed rate mortgage rates. Based on this confidence interval, would you conclude that there is a difference in the mean rates? 2. The Excel file Student Grades contains data on midterm and final exam grades in one section of a large statistics course. Construct a 95% confidence interval for the mean difference in grades between the midterm and final exams.