9.2 The quarterly sales (in 000) of greeting cards in a supermarket were: Quarter 1 2 3 4 Year 1 Year 2 Year 3 12.0 13.1 14.8 14.8 16.3 18.9 9.6 8.2 6.9 19.2 22.8 25.1 (a) Produce a time series plot of these figures. (b) Work out centred four-point moving averages for this series and plot them on your graph. 9.7 Building on your answers to Review question 9.2 use the multiplicative decomposition model to: (a) Find the seasonal factors for each quarter. (b) Calculate the MSD for the model. (c) By contrasting your answer to part (b) with the MSD for the additive model you obtained for Review question 9.6 part (b) state which is the better model for the greeting card sales series. 9.2 The quarterly sales (in 000) of greeting cards in a supermarket were: Quarter 1 2 3 4 Year 1 Year 2 Year 3 12.0 13.1 14.8 14.8 16.3 18.9 9.6 8.2 6.9 19.2 22.8 25.1 (a) Produce a time series plot of these figures. (b) Work out centred four-point moving averages for this series and plot them on your graph. 9.7 Building on your answers to Review question 9.2 use the multiplicative decomposition model to: (a) Find the seasonal factors for each quarter. (b) Calculate the MSD for the model. (c) By contrasting your answer to part (b) with the MSD for the additive model you obtained for Review question 9.6 part (b) state which is the better model for the greeting card sales series