Alcohol Percentage

Hey group! I’m trying to find the scientific of adding two different percentages of alcohol together does it divide or add or what?! I know it’s a dumb question, more so asking a groups who just enjoys alcohol, but if anyone has the knowledge, throw me a PM and educate me.

i.e. 13.9% ABV + 5% ABV = x

Is it 18.9% ABV?

Is it 16.4%

Or am i an idiot.