Question

How can you quickly calculate 20 percent of any bill amount?

Answer 1

10 times 2=20
so find 10% of the bill and double it

10% is easy because it is 1/10
just move decimal place over 1 palce

example
20% of 34.30
10% is 3.43
20% is double that or 6.86

Answer 2

Take it and divide it by 5, or you can multiply it by 2.