What is estimation?
To estimate means to find an answer that is close enough, without working it out exactly. We do this by rounding the numbers to make them easier to add, subtract or multiply.
Key idea
Round each number to a nearby tidy number (nearest ten, hundred or thousand), then do the easy calculation in your head.
Worked example
Estimate 297 + 402. Round to the nearest hundred: 297 → 300 and 402 → 400. So 300 + 400 = 700. The answer is about 700.
Why estimate?
Estimating helps us check if an answer makes sense. If a friend says 297 + 402 = 1 099, our estimate of 700 tells us that answer must be wrong. It is also handy when shopping: if three toys cost 198, 305 and 401 sen, we can round to 200, 300 and 400 to see we need about 900 sen before we pay.
Remember
- An estimate is close, not exact.
- Round first, then calculate.
- Use estimates to check your real answers.