everyone’s brain works differently

and I think those differences are very interesting. One aspect of this is how people do math in their heads, so I’d like to know how you do percentages either in your head or not (since not everybody can do it in their heads, and that’s okay).

If I need to figure out what 60% of 45 is, this is what I do in my head:
4.5 x 6 = 27

If I want to leave a 20% tip on a $26.50 bill, this is what I do in my head:
2.65 x 2 = 5.3 then 5.3 tip + $26.50 bill = $31.80.

So how do you calculate percentages?