[Megary]

My thinking is that if I add a spirit (tequila, rum, maybe both  ...etc.) to a finished beer at packaging, the new ABV would be a balancing equation of volumes and ABV's:
(Vol1*ABV1 + Vol2*ABV2 +Vol3*ABV3 etc.) / (Vol1+Vol2+Vol3 etc.)

Or is there more to it than that?  And if there is more to it than that is it really worth the extra effort in figuring it out?

[kramerog]

Your equation should work fine. There could be subtle changes in volume when mixing, but the equation will be close enough.

[Iliff Ave]

I think it should be as simple as a weighted average calculation. I added 4 oz of rum to a smaller batch and it bumped up the ABV by 0.2% according to weighted average.

[Megary]

I think it should be as simple as a weighted average calculation. I added 4 oz of rum to a smaller batch and it bumped up the ABV by 0.2% according to weighted average.

Weighted Average!  Yes, that's what they call it!  I think that's what my equation represents, but I'm way too far removed from algebra to remember the proper terminology. 

Thanks all.

[Iliff Ave]

I think it should be as simple as a weighted average calculation. I added 4 oz of rum to a smaller batch and it bumped up the ABV by 0.2% according to weighted average.

Weighted Average!  Yes, that's what they call it!  I think that's what my equation represents, but I'm way too far removed from algebra to remember the proper terminology. 

Thanks all.

I hear ya. I couldn't remember either although it seemed so simple. I'm sure I'll forget next time I go to do it...