Question

What is better 20$ or 20% off

Answer 1

20x(1-20%)
=20x80%
=20x0.8
=16
I think you mean that.
If it is , that's your answer.

Answer 2

Probably $20 dollars because depending on how much the item cost 20% could only be worth $5 for example 20% off of an item that cost $60 is only $12