Three-Digit Addition & Subtraction — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. 364 + 278 = 642.
364 + 278 = 642. Add ones: 4 + 8 = 12, write 2 carry 1. Add tens: 6 + 7 + 1 = 14, write 4 carry 1. Add hundreds: 3 + 2 + 1 = 6.
2. 825 - 467 = 358.
825 - 467 = 358. Subtract ones: 15 - 7 = 8 (borrow from tens). Subtract tens: 1 - 6 requires borrowing: 11 - 6 = 5. Subtract hundreds: 7 - 4 = 3.
3. 193 + 548 = 741.
193 + 548 = 741. Add ones: 3 + 8 = 11, write 1 carry 1. Add tens: 9 + 4 + 1 = 14, write 4 carry 1. Add hundreds: 1 + 5 + 1 = 7.
4. 700 - 386 = 314.
700 - 386 = 314. Borrow across zeros: 700 becomes 6-9-10. Subtract ones: 10 - 6 = 4. Subtract tens: 9 - 8 = 1. Subtract hundreds: 6 - 3 = 3.
5. 456 + 327 = 783.
456 + 327 = 783. Add ones: 6 + 7 = 13, write 3 carry 1. Add tens: 5 + 2 + 1 = 8. Add hundreds: 4 + 3 = 7.
6. 912 - 578 = 334.
912 - 578 = 334. Subtract ones: 12 - 8 = 4 (borrow from tens). Subtract tens: 0 - 7 requires borrowing: 10 - 7 = 3. Subtract hundreds: 8 - 5 = 3.
7. About how much is 498 + 312 when you round each to the nearest hundred? 800.
498 rounds to 500 and 312 rounds to 300, so 500 + 300 = 800.
8. 635 - 289 = 346.
635 - 289 = 346. Subtract ones: 15 - 9 = 6 (borrow from tens). Subtract tens: 2 - 8 requires borrowing: 12 - 8 = 4. Subtract hundreds: 5 - 2 = 3.
9. About how much is 703 - 298 when you round each to the nearest hundred? 400.
703 rounds to 700 and 298 rounds to 300, so 700 - 300 = 400.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
247 + 385
→ 632
642
900 - 456
→ 444
457
163 + 479
→ 642
444
814 - 357
→ 457
632
247 + 385 = 632, 900 - 456 = 444, 163 + 479 = 642, and 814 - 357 = 457.