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).