An estimate is a quick, close answer. Round each number to the place the question asks, then add or subtract the rounded numbers in your head. To round, look at the digit just after that place: 5 or more rounds up, 4 or less rounds down. For the leading place, round each number to the place of its first digit.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- estimate
- a close answer found with friendly numbers
- leading place
- the place value of a number's first digit
Worked examples
Estimate 47 + 38 by rounding each number to the nearest ten.
- 1.47 rounds to 50 and 38 rounds to 40.
- 2.50 + 40 = 90.
= 90
Estimate 487 + 312 by rounding each number to the nearest hundred.
- 1.487 rounds to 500 and 312 rounds to 300.
- 2.500 + 300 = 800.
= 800
Estimate 4327 − 689 by rounding each number to its leading place.
- 1.4327 rounds to 4000 and 689 rounds to 700.
- 2.4000 − 700 = 3300.
= 3300
For parents
Method: Round, then calculate
What to say: What does each number round to? Is your estimate close to what you expect?
Common mistakes:
- Rounds by chopping off the last digits (always down).
- Works out the exact answer instead of estimating.
- Rounds only the first number and uses the second exactly.
- Rounds to a different place from the one asked (tens instead of hundreds, or both numbers to the larger number's leading place).