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Use estimation to check an answer

Estimation involves replacing numbers with nearby, easier values—often the nearest ten or hundred—to predict a reasonable sum or difference, then comparing that estimate with an exact answer for numbers within 1,000. The learner understands that an estimate is not usually the exact result and uses its size and place-value relationships to identify answers that are clearly unreasonable, building a foundation for checking calculations with larger numbers and other operations.

Detailed Explanation: Use estimation to check an answer

An estimate is a close, easier number that helps you decide whether an exact answer makes sense.

Example: Check the answer to

247+368=615247+368=615
  1. Round each number to the nearest hundred.

    • 247247 is close to 200200.
    • 368368 is close to 400400.
  2. Add the rounded numbers.

200+400=600200+400=600

So, the estimate is about 600600.

  1. Compare the estimate with the exact answer. The exact answer is 615615. This is close to 600600, so the answer is reasonable.

The estimate does not have to be exact. It helps you notice answers that are far too large or far too small. For example, 247+368247+368 could not be 915915 because 915915 is much larger than the estimate of about 600600.

Learn by doing: Use estimation to check an answer

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Addition - Estimate Sum - 3 & 2 Digit


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