The monthly gasoline demand (in thousands of barrels/day) for Yukong Oil Company of South Korea for the period from January 1986 to September 1996 is contained in Table P-17.

a. Plot the gasoline demand time series. Do you think an additive or a multiplicative decomposition would be appropriate for this time series? Explain.
b. Perform a decomposition analysis of gasoline demand.
c. Interpret the seasonal indexes.
d. Forecast gasoline demand for the last three months of 1996.

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TABLE P17 Month 1986 1987 1988 19891990 1991 1992993 1994 995 1996 anuary5.5 204 26.9 36 21 64 82.3 027 222 1458 170.0 February 178 20.8 294 39.0 53.1 681 83.6 102.2 1214 1444 1763 March April May June July August September 229 25.8 390 52.2 68 84.4 1015 124.6 1499 163 1922 October 18.1 222 29 685 85.5 104.7 125,6 45.2 1742 20.5 241 324 43 84 72.3 910 108.9 129.7 1486 171 213 255 333 466617 741 921 1122 133.6 13.7 1853 198 259 345 46. 0 77.6 95.8 19,7 137.5 1579 1827 20.5 26 34.8 485 655 79 983 1135 143.0 6. 1970 22.3 275 39.1 526 06.7 02 1204 149.0 184.2 2161 21.1 9.8 363 508 4 98 7 1395 1554 November 22.0274 375 519 688 R 206 147.7 168.9 December 228 9.7 39.7 8817 102 124 1547 178.3