The Manager of a Fast Food Restaurant Wants to Determine

Essay

The manager of a fast food restaurant wants to determine how sales in a given week are related to the number of discount vouchers (#) printed in the local newspaper during the week. The number of vouchers and sales ($000s) from 10 randomly selected weeks is given below with the predicted sales.
Calculate the residuals. $$\begin{array} { | c | c | c | c | } \hline \text { Observation } & \text { Sales } & \text { Predicted Sales } & \text { Residuals } \\\hline 1 & 12.8 & 13.4147 & - 0.6147 \\\hline 2 & 15.4 & 14.8000 & 0.6000 \\\hline 3 & 13.9 & 13.8765 & 0.0235 \\\hline 4 & 11.2 & 12.9529 & - 1.7529 \\\hline 5 & 18.7 & 20.3412 & - 1.6412 \\\hline 6 & 17.9 & 16.1853 & 1.7147 \\\hline 7 & 16.8 & 15.2618 & 1.5382 \\\hline 8 & 15.9 & 14.3382 & 1.5618 \\\hline 9 & 11.5 & 12.9529 & - 1.4529 \\\hline 10 & 13.9 & 13.8765 & 0.0235 \\\hline\end{array}$$ Plot the residuals against the predicted values of y. Does the variance appear to be constant?