Quick2U, a delivery company, would like to standardize its delivery charge model for shipments such that customers will better understand their delivery costs. Three variables are used: (1) distance (one-way), (2) shipment weight, and (3) number of boxes. A sample of 30 recent deliveries is collected; a portion of the data is shown in the accompanying table.
Charge ($) Distance (miles) Weight (lbs) Boxes(units)
92.50..................29......................183....................1
157.60.................96......................135....................3
⋮..........................⋮..........................⋮.....................⋮
143.00.................47......................117....................7
a. Estimate the model Charge = β0 + β1Distance + β2Weight + β3Boxes + ε and examine the joint and individual significance of the explanatory variables at the 1% level.
b. Is there any evidence of multi-collinearity?
c. Examine the residual plots for evidence of heteroskedasticity.