How to get the New Cargo Density?

This is one of the simple ways to get New Density.
When loading two different cargoes with different densities into a same tank.

By scientific calculator or by microsoft excel worksheet.

* = Multiply
/  = Divide

New Density =((First Cargo Volume*First Cargo Density)+(Total Cargo Volume - First Cargo Volume) * 2nd Cargo Density)/Total Cargo Volume