Subtraction strategies
Lesson 9 of 12
Checking with the inverse
Objective. Use addition to check a subtraction answer.
The key idea
Addition and subtraction undo each other. If a − b = c then c + b must give back a.
Worked example
Check that 265 is the answer to 402 − 137.
- 1Add the answer to the number taken away: 265 + 137.
- 2265 + 137 = 402.
- 3It matches the original number.
Answer: Correct
Practice
Each question comes with a picture and a listen button. Try it first, then reveal the answer.
Common mistake. Adding the wrong pair of numbers when checking.
Your progress
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