Three-Digit Addition and Subtraction — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. 529 + 384 = 913.
Add ones: 9 + 4 = 13, write 3 and carry 1. Add tens: 2 + 8 + 1 = 11, write 1 and carry 1. Add hundreds: 5 + 3 + 1 = 9. The sum is 913.
2. 741 - 365 = 376.
Subtract ones: 1 < 5, so borrow: 11 - 5 = 6. Tens: 3 - 6 needs borrowing: 13 - 6 = 7. Hundreds: 6 - 3 = 3. The difference is 376.
3. 268 + 457 = 725.
Add ones: 8 + 7 = 15, write 5 and carry 1. Add tens: 6 + 5 + 1 = 12, write 2 and carry 1. Add hundreds: 2 + 4 + 1 = 7. The sum is 725.
4. 800 - 529 = 271.
800 has zeros in the ones and tens, so borrow across both: 10 - 9 = 1, 9 - 2 = 7, 7 - 5 = 2. The difference is 271.
5. 347 + 486 = 833.
Add ones: 7 + 6 = 13, write 3 and carry 1. Add tens: 4 + 8 + 1 = 13, write 3 and carry 1. Add hundreds: 3 + 4 + 1 = 8. The sum is 833.
6. 654 - 279 = 375.
Subtract ones: 4 < 9, borrow: 14 - 9 = 5. Tens: 4 - 7 needs borrowing: 14 - 7 = 7. Hundreds: 5 - 2 = 3. The difference is 375.
7. About how much is 612 + 289 when you round each to the nearest hundred? 900.
Round 612 to 600 and 289 to 300. Then 600 + 300 = 900, so the best estimate is 900.
8. 503 - 178 = 325.
Since 3 < 8 and there is a 0 in the tens, borrow across the zero: 13 - 8 = 5, 9 - 7 = 2, 4 - 1 = 3. The difference is 325.
9. About how much is 847 - 392 when you round each to the nearest hundred? 500.
Round 847 to 900 (since 47 is close to 50) and 392 to 400. Then 900 - 400 = 500, giving an estimate of about 500.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
395 + 268
→ 663
763
806 - 349
→ 457
437
174 + 589
→ 763
663
920 - 483
→ 437
457
Correct matches: 395 + 268 → 663; 806 - 349 → 457; 174 + 589 → 763; 920 - 483 → 437.