11.74 One fact that must be considered in developing a shipping system that is beneficial to both the customer and the seller is time of delivery.

A manufacturer of farm equipment can ship its products by either rail or truck. Quadratic models are thought to be adequate in relating time of delivery to distance traveled for both modes of transportation. Consequently, it has been suggested that the following model be fit:

where a What hypothesis would you test to determine whether the data indicate that the quadratic distance term is useful in the model, that is, whether curvature is present in the relationship between mean delivery time and distance?

b What hypothesis would you test to determine whether there is a difference in mean delivery time by rail and by truck?