Estimation and Rounding — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. Round each factor to the nearest ten: 32 x 19 is approximately 600.
Using compatible numbers, 30 x 20 = 600, which is a reasonable estimate of the product.
2. Estimate the product: 48 x 21 is approximately 1,000.
50 x 20 = 1,000, giving a clean approximate value for 48 x 21.
3. Estimate: 73 x 38 is approximately 2,800.
70 x 40 = 2,800. These compatible numbers make the calculation easy.
4. Estimate: 19 x 41 is approximately 800.
20 x 40 = 800, an efficient estimate of 19 x 41.
5. Estimate: 62 x 89 is approximately 5,400.
60 x 90 = 5,400, a quick estimate of the product.
6. Estimate: 28 x 52 is approximately 1,500.
30 x 50 = 1,500, a simple compatible-number estimate.
7. Estimate: 47 x 79 is approximately 4,000.
50 x 80 = 4,000, a reasonable estimate using compatible numbers.
8. Estimate: 91 x 11 is approximately 900.
90 x 10 = 900, an easy compatible-number estimate.
9. Estimate: 38 x 62 is approximately 2,400.
40 x 60 = 2,400, a clean estimate of the product.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Estimate of 22 x 39
→ 800
1,000
Estimate of 51 x 18
→ 1,000
2,400
Estimate of 78 x 31
→ 2,400
800
Estimate of 43 x 58
→ 2,500
2,500
22 x 39 is about 20 x 40 = 800. 51 x 18 is about 50 x 20 = 1,000. 78 x 31 is about 80 x 30 = 2,400. 43 x 58 is about 40 x 60 = 2,400, but using 2,500 reflects rounding 43 to 50.