FILE Consider the following 20 observations, representing quarterly information for 5 years. The data are also on the text website, labeled Exercise 18.20.

Year Quarter 1 Quarter 2 Quarter 3 Quarter 4 1 8.37 12.78 8.84 15.93 2 10.03 12.48 8.91 24.81 3 9.61 9.65 15.93 22.00 4 8.80 11.45 6.79 10.16 5 7.46 10.58 13.35 19.77

a. Calculate the 4-quarter centered moving average.

b. Calculate the ratio-to-moving average.

c. Calculate and interpret the seasonal indices for quarters 1 and 4.