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

Question

hero · Answer

Suppose you have $25. Move the decimal one place to the left to get 10%. Now you have $2.50 Multiply that by 2 to get 20%. Now you have $5

solomonzelman · Answer

divide by 5 (I suppose).

solomonzelman · Answer

either way... would have been better using an american computer and keyboard tho.
bye:)

terenzreignz · Answer

Will it be easier to do Hero's method in reverse?
ie Double it first and then move the dot?

hero · Answer

If you want to find 30% of $25, again move the decimal one to the left: $2.50. Then multiply by 3 to get $7.50

hero · Answer

The point is, it is possible to do this in your head without a calc.

hero · Answer

Finding percentages of numbers can be a "mental math" activity.