Calculating Weighted Averages in Pivot Tables

Does anyone know the best way to have a pivot table return a weighted average instead of the standard average? Within the attached spreadsheet I have a pivot tab. I'd like to create a weighted average for the APR. Currently it shows 4.62%. On the data tab I calulated the weighted average at 4.11%. Is there anyway to get the 4.11% value to show in the pivot table? Thanks