Mental math

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%.

(source – The Skills We’ve Lost to Technology (and How to Get Them Back))

Chris Blakeley - math in the body, https://flic.kr/p/eFnc3H
Chris Blakeley – math in the body, https://flic.kr/p/eFnc3H

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