Grade 3 Mental Math: Compensation Strategy

Worked examples

Real problems from the practice worksheets, solved one step at a time.

1. Example 1

   298 + 347 = ?

   1. Line up the numbers by place value.
   2. Add each column from right to left.
   3. Ones: 8 + 7 = 15. Write 5, carry 1.
   4. Tens: 9 + 4 + 1 (carried) = 14. Write 4, carry 1.
   5. Hundreds: 2 + 3 + 1 (carried) = 6
   6. The answer is 645.

   Answer: 645

2. Example 2

   31 + 52 = ?

   1. Break apart both numbers by place value.
   2. 31 = 30 + 1
   3. 52 = 50 + 2
   4. Add the tens: 30 + 50 = 80
   5. Add the ones: 1 + 2 = 3
   6. Combine: 80 + 3 = 83

   Answer: 83

3. Example 3

   298 + 129 = ?

   1. Line up the numbers by place value.
   2. Add each column from right to left.
   3. Ones: 8 + 9 = 17. Write 7, carry 1.
   4. Tens: 9 + 2 + 1 (carried) = 12. Write 2, carry 1.
   5. Hundreds: 2 + 1 + 1 (carried) = 4
   6. The answer is 427.

   Answer: 427