Consider the follow ing 10 observations on the response variable y and the explanatory variable x.

9.42 4.88 3.36 3.28 1.67 7.35 6.30 4.67 9.33 5.04 1

9 5 5 4 10 3 10 11 8

a. Plot the above data and estimate the linear and the quadratic regression models.

b. Use the appropriate numerical measure to justify which model fits the data best.

c. Given the best-fitting model, predict y for x = 4 , 6, and 12.

d. Find x at which the quadratic equation reaches a m inim um or maximum .