Skill: Check addition with subtraction

When you add two numbers, you can check your answer by subtracting either addend from the sum. Addition and subtraction are inverse operations, which means they undo each other.

Example:

$$247+158=405$$

Check the answer by subtracting one addend:

1. Write the sum, $(405)$, on top.
2. Write the addend, $(158)$, underneath, lining up the ones, tens, and hundreds.
3. Subtract.

$$\begin{array}{r} 405\\ -158\\ \hline 247 \end{array}$$

The subtraction gives $(247)$, which is the other addend. So the addition is correct:

$$405-158=247$$

You could also check by subtracting $(247)$:

$$405-247=158$$

If the subtraction does not give the other addend, recheck your place values and any regrouping in the addition.