Mental math is by no means required to survive in the world, but being able to do a few basic calculations in your head makes life a lot easier. For example, calculating a tip is all about basic percentages and is simple to do in your head:
- To find 5%, find 10% and divide it in two.
- To find 15%, find 10%, then add 5%.
- To find 20%, find 10% and double it.
- To find 25%, find 50% and then halve it.
- To find 60%, find 50% and add 10%.
- To find 75%, find 50% and add 25%.