Question 4 (13 marks) Give your answers to 3 decimal places where necessary. (a) Quarterly sales (in thousand dollars) of a tablet computer shop over 4 years are shown in the following table. Find the missing values a, b, c, d, e, f, g, h and i (in thousand dollars). (4.5 marks) x Year Quarter Sales 4 Quarter-MA Seasonal Difference 1 2018 1 120 2 2 370 3 3 320 232.50 252.500 67.500 4565 4 120 272.50 287.500 -167.500 2019 1 280 302.50 320.000 -40.000 2 490 337.50 350.000 140.000 7 3 460 362.50 377.500 82.500 8 4 220 392.50 421.250 -201.250 9 2020 1 400 450.00 476.250 -76.250 10 2 720 502.50 518.750 201.250 11 3 670 535.00 a f 12 4 350 570.00 b g 13 2021 1 540 590.00 C h 14 2 tel:2%20720%203%20670%204%20350%201%20540 15 3 760 657.50 e 16 4 530 (b) Assume an additive model is suitable to describe the data. The seasonal effects have already calculated with some cells missing. Find the missing values m, n, o, p, q, r, s, t and u (in thousand dollars). (4.5 marks) Quarter 2018 2019 2020 2021 Average Seasonal Variation 1 -40.000 -76.250 0 -59.167 r 2 140.000 m P 168.750 S 3 67.500 82.500 n 89.167 t 4 -167.500 -201.250 -230.000 q u sum = -0.833 0.000 adjustment = 0.208