Petrol Sales in Newcastle Have Been Recorded Over the Past

Essay

Petrol sales in Newcastle have been recorded over the past 10 months as shown below. $$\begin{array} { | l | c c c c c c c c c c | } \hline \text { Month } & \text { Jan } & \text { Feb } & \text { Mar } & \text { Apr } & \text { May } & \text { Jun } & \text { Jul } & \text { Aug } & \text { Sep } & \text { Oct } \\\hline \text { Sales } & 75 & 72 & 81 & 92 & 90 & 105 & 112 & 107 & 110 & 93 \\\hline\end{array}$$ a. Compute the five-month moving average.
b. Calculate the four-month moving average, and four-month centred moving average.
c. Compute the exponentially smoothed sales with w = 0.4 and w = 0.8.
d. Draw the time series and the two sets of exponentially smoothed values. Does there appear to be a trend component in the time series?