A 20% tip would mean that you would give how much you paid for the foods, plus 20% of that food price.
Example:
Let's say I went to a sit down restaurant and the price was %50. I would still pay the $50, but will pay the 20% tip. In order to do that, multiply 0.2 by 50. 1%=0.01. Then you would pay $10 for tip. Now, add 50 to 10 and get 60. Therefore, %60 is how much I'll pay.
