lesson
Does the answer make sense?
1 · Learn
An estimate is a sensible approximate answer. It helps you notice a result that is much too large or small.
An inverse calculation checks more exactly. Addition and subtraction undo each other. An estimate alone does not prove an exact answer is correct.
2 · Worked example
If someone says 198 + 305 = 903, an estimate near 500 shows a problem. I then calculate and check the exact answer.
3 · Your turn
A library has 275 books and receives 124 more. Find the total and check by subtraction.
Check your answer
399 books. 399 − 124 = 275.
4 · Apply your learning
Write a calculation with an intentionally wrong answer. Explain which check reveals the error.
Adult guidance and safety
Use objects or a drawn model before relying on a rule. Explain each step, check the units and revisit with varied examples. An adult can read the instructions without supplying the answer.
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