1. Breaking down numbers

Here are two different examples where breaking down numbers can help you add or subtract in your head.

• 40 + 67
  40 + 67 is the same as 40 + 60 + 7, which is 100 + 7, which is 107.
• Find the difference between 38 and 63
  Count on from 38 to 40 and keep that 2 in your head. Now count on from 40 to 60, which is 20, and from 60 to 63, which is 3. Add the 2, 20 and 3 to make 25.

The difference between 38 and 63 is 2 + 20 + 3 = 25