For those having difficulty calculating the amount of tip to leave at a restaurant, here's a quick and easy way. If you want to leave 15%, take 10% and then half of that 10% and add them together.

Total bill : $24

10% = 2.40
+ 5%   1.20
Tip =   $3.60

If you wish to leave 20% and you don't feel like multiplying, just take 10% and double it.

10% is simple to get. Just move the decimal point over 1 to the left. 10% of 25.78 is 2.58 (rounded off).