🔢 MathLevel 1Lesson 16
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Checking Our Work

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Learning Objectives

  • 1Use the inverse operation to check addition and subtraction answers
  • 2Write a matching check sentence for any addition or subtraction fact
  • 3Spot and correct a wrong answer using a check
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Mini Lesson

Good mathematicians don't just find an answer — they check it! The fastest way to check is to use the opposite operation.

What is the inverse operation?

  • Addition and subtraction are inverse operations — they undo each other.
  • Example: 3 + 4 = 7 → check it by subtracting: 7 − 4 = 3 ✓
  • If the check gives back the number you started with, your answer is correct.

Check addition with subtraction

  • Solve: 5 + 4 = 9
  • Check: 9 − 4 = 5 — that's the first number, so ✓ correct!
  • Or check: 9 − 5 = 4 — that's the second number, so ✓ correct!

Check subtraction with addition

  • Solve: 8 − 3 = 5
  • Check: 5 + 3 = 8 — that's the starting number, so ✓ correct!
  • Rule: answer + the number subtracted = the starting number.
Checking addition using subtractionTwo arrows forming a loop: 3 + 4 = 7 going right, then 7 − 4 = 3 returning left, showing addition and subtraction undo each other.Check Addition → Subtract3+ 473 + 4 = 77 − 4 = 3 ✓Subtractto check!You get back to 3 → correct!
The forward arrow shows 3 + 4 = 7. The return arrow shows 7 − 4 = 3, confirming the answer.
Checking subtraction using additionA flow showing 8 minus 3 equals 5, then 5 plus 3 equals 8, confirming the subtraction.Check Subtraction → Add8 − 3 = ?8 − 3 = 55 + 3 = 8 ✓Answer= 5Add backthe 3= 8 ✓
To check 8 − 3 = 5, add the answer and the subtracted number: 5 + 3 = 8. Getting back to 8 confirms the answer.
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Ask yourself: "Can I use the opposite operation to get back to where I started?"

Vocabulary
Check
A way to test if your answer is righte.g. I check 3 + 4 = 7 by doing 7 − 4.
Inverse operation
The opposite math action that undoes anothere.g. Subtraction is the inverse of addition.
Undo
To take back what you just dide.g. Subtracting 4 undoes adding 4.
Correct
Right — matches what was expectede.g. My answer is correct because the check works.
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← Lesson 15: Addition and Subtraction in Real LifeLesson 17: Naming 2D Shapes →