Mortgage payments: The following table presents interest rates, in percent, for 30-year and 15-year fixed-rate mortgages, for January through December 2012.

30-Year 15-Year 30-Year 15-Year

3.92 3.20 3.55 2.85

3.89 3.16 3.60 2.86

3.95 3.20 3.47 2.78

3.91 3.14 3.38 2.69

3.80 3.03 3.35 2.66

3.68 2.95 3.35 2.66

a. Compute the least-squares regression line for predicting the 15-year rate from the 30-year rate.

b. Construct a scatterplot of the 15-year rate (y) versus the 30-year rate (x). Graph the least-squares regression line on the same axes.

c. Is it possible to interpret the y-intercept? Explain.