Conditional calculation in Matrix visual using Excel's SUMPROD function

Hello PBI Community,
Greg_Deckler 

I'm an intermediate level user struggling to do some hocus pocus with a Matrix visual. When Class column is expanded, Average column does an average (i.e., 5, 10, 5, 20), but when collapsed the total displayed in the column is the calculation of the Excel SUMPROD function (i.e., 12). I've been trying and reading on my own for a couple of weeks but haven't had any luck thus far.

Example:

Any help is greatly appreciated