Estimation (Intro) — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. Round 38 to the nearest 10: 40
38 has ones digit 8, which is 5 or more, so 38 rounds up to 40.
2. Round 71 to the nearest 10: 70
71 has ones digit 1, which is less than 5, so 71 rounds down to 70.
3. Estimate 28 + 41 by rounding first: 70
28 rounds to 30 and 41 rounds to 40. Then 30 + 40 = 70, so the estimate is 70.
4. Estimate 52 + 19 by rounding first: 70
52 rounds to 50 and 19 rounds to 20. Then 50 + 20 = 70, so the estimate is 70.
5. Estimate 63 - 21 by rounding first: 40
63 rounds to 60 and 21 rounds to 20. Then 60 - 20 = 40, so the estimate is 40.
6. Estimate 47 + 32 by rounding first: 80
47 rounds to 50 and 32 rounds to 30. Then 50 + 30 = 80, so the estimate is 80.
7. Estimate 88 - 39 by rounding first: 50
88 rounds to 90 and 39 rounds to 40. Then 90 - 40 = 50, so the estimate is 50.
8. Round 54 to the nearest 10: 50
54 has ones digit 4, which is less than 5, so 54 rounds down to 50.
9. Round 46 to the nearest 10: 50
46 has ones digit 6, which is 5 or more, so 46 rounds up to 50.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
23
→ 20
20
27
→ 30
30
41
→ 40
40
48
→ 50
50
23 rounds down to 20. 27 rounds up to 30. 41 rounds down to 40. 48 rounds up to 50.