(a) State the classical decomposition (additive and standardized) for a time series, say {yt}. Characterize each component briefly. [4 marks] (b) Outline a procedure that seasonally adjusts a time series, say {yt}. [5 marks] (c) The following table contains the quarterly retail sales of a software company from 1998q1 to 1999q4. The MA(4)-smoothed series is also included. Retail Sales 1998q1–1999q4 98q1 98q2 98q3 98q4 99q1 99q2 99q3 99q4 Actual 25.9 18.0 11.0 26.3 21.2 13.3 13.2 26.6 MA(4) 20.3 19.1 18.0 18.5 18.6 Here MA(4) is defined as (yt−2 + yt−1 + yt + yt+1)/4. Use the MA(2*4) smoother to estimate the trend series. Report the trend series and the de-trended series with corresponding timing (ie, with an appropriate year and quarter). [3 marks] (d) The following table contains the mont