Adding in your head

For simple numbers, you can try to add them in your head.

You can make it easier by:

• Breaking up numbers

  40 + 67 is the same as
  40 + 60 + 7, which is
  107

• Rounding numbers

  42 + 89 is the same as
  (40 + 80) + (2 + 9), which is
  120 + 11, which is
  131