Three-Digit Addition and Subtraction — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. 438 + 275 = 713.
Add ones: 8 + 5 = 13, write 3 and carry 1. Add tens: 3 + 7 + 1 = 11, write 1 and carry 1. Add hundreds: 4 + 2 + 1 = 7. The sum is 713.
2. 962 - 487 = 475.
Subtract ones: 2 < 7, borrow: 12 - 7 = 5. Tens: 5 - 8 needs borrowing: 15 - 8 = 7. Hundreds: 8 - 4 = 4. The difference is 475.
3. 156 + 678 = 834.
Add ones: 6 + 8 = 14, write 4 and carry 1. Add tens: 5 + 7 + 1 = 13, write 3 and carry 1. Add hundreds: 1 + 6 + 1 = 8. The sum is 834.
4. 710 - 364 = 346.
Subtract ones: 0 < 4, borrow from the tens: 10 - 4 = 6. Tens: 0 - 6 needs borrowing from hundreds: 10 - 6 = 4. Hundreds: 6 - 3 = 3. The difference is 346.
5. 583 + 249 = 832.
Add ones: 3 + 9 = 12, write 2 and carry 1. Add tens: 8 + 4 + 1 = 13, write 3 and carry 1. Add hundreds: 5 + 2 + 1 = 8. The sum is 832.
6. 845 - 568 = 277.
Subtract ones: 5 < 8, borrow: 15 - 8 = 7. Tens: 3 - 6 needs borrowing: 13 - 6 = 7. Hundreds: 7 - 5 = 2. The difference is 277.
7. About how much is 387 + 214 when you round each to the nearest hundred? 600.
Round 387 to 400 and 214 to 200. Then 400 + 200 = 600, so the best estimate is 600.
8. 731 - 456 = 275.
Subtract ones: 1 < 6, borrow: 11 - 6 = 5. Tens: 2 - 5 needs borrowing: 12 - 5 = 7. Hundreds: 6 - 4 = 2. The difference is 275.
9. About how much is 919 - 503 when you round each to the nearest hundred? 400.
Round 919 to 900 and 503 to 500. Then 900 - 500 = 400, so the best estimate is 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.
467 + 356
→ 823
753
853 - 478
→ 375
436
219 + 534
→ 753
375
701 - 265
→ 436
823
Correct matches: 467 + 356 → 823; 853 - 478 → 375; 219 + 534 → 753; 701 - 265 → 436.