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Check addition with subtraction

Within whole numbers through 1,000, addition and subtraction are inverse operations: if a+b=ca+b=c, then subtracting either addend from cc should recover the other, allowing an addition result to be verified and errors in place-value regrouping to be identified. The understanding applies to standard numerical equations and related unknown-addend situations, not to negative numbers, decimals, fractions, or formal algebraic generalizations.

Detailed Explanation: 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=405247+158=405

Check the answer by subtracting one addend:

  1. Write the sum, (405)(405), on top.
  2. Write the addend, (158)(158), underneath, lining up the ones, tens, and hundreds.
  3. Subtract.
405−158247\begin{array}{r} 405\\ -158\\ \hline 247 \end{array}

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

405−158=247405-158=247

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

405−247=158405-247=158

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

Learn by doing: Check addition with subtraction

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    Addition - Missing Value, 3 Digit, 2 Numbers

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