operations · Year 5 · AC9M5N08
Estimate a product
Round each factor to a friendly number, then multiply the rounded numbers using a basic fact and the zeros. For 38 × 7, 38 rounds to 40, and 40 × 7 = 280. The estimate tells you roughly how big the exact answer should be, so you can check your working.
Sample questions
Estimate 17 × 5 by rounding 17 to the nearest ten.
- 17 rounds to 20.
- Basic fact: 2 × 5 = 10. Then put on 1 zero.
- 20 × 5 = 100, so the estimate is 100.
Answer: 100
Estimate 32 × 5 by rounding 32 to the nearest ten.
- 32 rounds to 30.
- Basic fact: 3 × 5 = 15. Then put on 1 zero.
- 30 × 5 = 150, so the estimate is 150.
Answer: 150
Estimate 46 × 4 by rounding 46 to the nearest ten.
- 46 rounds to 50.
- Basic fact: 5 × 4 = 20. Then put on 1 zero.
- 50 × 4 = 200, so the estimate is 200.
Answer: 200