What is estimation?
Estimation means finding an answer that is close to the exact one, but quicker to work out. We often estimate by rounding each number first, then calculating with the rounded numbers. Estimation is very useful when shopping, because it helps us check quickly that we have enough money before we pay.
How to estimate
Round each number to the nearest ten, hundred or thousand, then add, subtract, multiply or divide. Choose a place that keeps the numbers easy to work with. Then compare your estimate with the exact answer to see that it makes sense.
Key idea
Round first, then calculate. An estimate is not the exact answer — it is a sensible, close value.
Worked example
Estimate 297 + 405. Round to the nearest hundred: 297 → 300 and 405 → 400. So 300 + 400 = 700. The exact answer is 702, so 700 is a good estimate.
Remember
- Estimates are quick and close, not exact.
- Round each number before calculating.
- Use estimation to check if an answer is sensible.