Check Subtraction With Addition

Check subtraction by addition

Subtraction and addition are inverse operations. That means you can check a subtraction by using the answer to build an addition sentence.

How to check

1. Start with the subtraction sentence.
2. Use the answer as one addend.
3. Add it to the number you subtracted.
4. If the sum matches the original starting number, the subtraction is correct.

Example method

For a subtraction like A - B = C:

• Check with C + B = A

This works because subtracting B from A leaves C, so adding B back should recover A.

Good habit

Write the check immediately after finishing the subtraction. If the addition does not equal the starting number, go back and rework the subtraction carefully.

Quick check

• Does the addition use the same two numbers from the subtraction?
• Does it return to the first number?

If yes, your subtraction is verified.