operations · Year 4 · AC9M4N07
Estimate sums and differences
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.
Sample questions
Estimate 83 + 84 by rounding each number to the nearest ten.
- 83 rounds to 80 and 84 rounds to 80.
- 80 + 80 = 160, so the estimate is 160.
Answer: 160
Estimate 63 − 52 by rounding each number to the nearest ten.
- 63 rounds to 60 and 52 rounds to 50.
- 60 − 50 = 10, so the estimate is 10.
Answer: 10
Estimate 78 − 72 by rounding each number to the nearest ten.
- 78 rounds to 80 and 72 rounds to 70.
- 80 − 70 = 10, so the estimate is 10.
Answer: 10