Estimation Strategies — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. Estimate 47 times 312 by rounding to 50 and 300 to get 15000.
50 times 300 equals 15,000, giving a quick estimate close to the true product.
2. Estimate 612 divided by 31 using compatible numbers 600 and 30 to get 20.
600 divided by 30 equals 20, a compatible-number estimate close to the real quotient.
3. Estimate 89 times 41 by rounding to 90 and 40 to get 3600.
90 times 40 equals 3,600, providing a fast and reasonable product estimate.
4. A rectangle is 38 cm by 22 cm. Estimate the perimeter using 40 and 20 to get 120 cm.
Two times forty plus two times twenty equals 120, an easy perimeter estimate.
5. Estimate 7,812 divided by 38 with compatible numbers 8000 and 40 to get 200.
8,000 divided by 40 equals 200, giving a compatible-number quotient estimate.
6. Estimate the area of a 19 by 41 rectangle using 20 and 40 to get 800 square units.
20 times 40 equals 800 square units, a quick and close area estimate.
7. Estimate 58 times 23 by rounding both factors to get 1200.
60 times 20 equals 1,200, a fast estimate near the actual product.
8. Estimate 4,210 divided by 68 using compatible numbers 4200 and 70 to get 60.
4,200 divided by 70 equals 60, a clean compatible-number quotient estimate.
9. Estimate the perimeter of a 49 cm by 31 cm rectangle using 50 and 30 to get 160 cm.
Two times fifty plus two times thirty equals 160, a tidy perimeter estimate.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
48 times 21
→ About 1000
About 1000
789 divided by 41
→ About 20
About 20
29 cm by 11 cm area
→ About 300
About 300
6,210 divided by 31
→ About 200
About 200
Rounding to friendly numbers makes products and quotients quick to estimate accurately.