number · Year 6 · AC9M6N08
Estimating with decimals, fractions and percentages
An estimate uses friendly numbers so you can calculate in your head. Round each number to the nearest whole number, ten or dollar, as the question says: 5 or more rounds up. Then calculate with the rounded numbers. For percentages, find 10% by dividing by 10, 50% by halving and 25% by halving twice. For a fraction, divide by the bottom number and multiply by the top. Estimates are close to the exact answer, not equal to it.
Sample questions
Estimate 8.7 × 1.4 by rounding each number to the nearest whole number first.
- 8.7 rounds to 9. 1.4 rounds to 1.
- 9 × 1 = 9.
- The estimate is 9.
Answer: 9
Estimate 20.2 + 31.1 by rounding each number to the nearest whole number first.
- 20.2 rounds to 20. 31.1 rounds to 31.
- 20 + 31 = 51.
- The estimate is 51.
Answer: 51
Estimate 49.7 + 32.8 by rounding each number to the nearest whole number first.
- 49.7 rounds to 50. 32.8 rounds to 33.
- 50 + 33 = 83.
- The estimate is 83.
Answer: 83