Splitting up numbers

Splitting up numbers is a good method to use for both addition and subtraction. It is sometimes called partitioning.

Addition

Take a look at this addition sum:
      80 + 49

To make it easier, split the 49 into 40 + 9. This makes the sum:
      80 + 40 + 9 = 129

First, add the first two numbers:
      80 + 40 = 120

Then add the result of that sum to the third number to get the answer:
      120 + 9 = 129

Subtraction

Take a look at this subtraction sum:
      150 - 34

To make it easier, split the - 34 into 30 - 4. This makes the sum:
      150 - 30 - 4

First, subtract the 30 from 150:
      150 - 30 = 120

Then, subtract the 4 from the 120 to get the answer:
      120 - 4 = 116