Three-Digit Addition & Subtraction — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. 529 + 347 = 876.
529 + 347 = 876. Add ones: 9 + 7 = 16, write 6 carry 1. Add tens: 2 + 4 + 1 = 7. Add hundreds: 5 + 3 = 8.
2. 641 - 275 = 366.
641 - 275 = 366. Subtract ones: 11 - 5 = 6 (borrow from tens). Subtract tens: 3 - 7 requires borrowing: 13 - 7 = 6. Subtract hundreds: 5 - 2 = 3.
3. 278 + 465 = 743.
278 + 465 = 743. Add ones: 8 + 5 = 13, write 3 carry 1. Add tens: 7 + 6 + 1 = 14, write 4 carry 1. Add hundreds: 2 + 4 + 1 = 7.
4. 803 - 518 = 285.
803 - 518 = 285. Subtract ones: 13 - 8 = 5 (borrow across zero). Subtract tens: 9 - 1 = 8. Subtract hundreds: 7 - 5 = 2.
5. A school has 356 red books and 478 blue books. How many books in all? 834.
356 + 478 = 834. Add ones: 6 + 8 = 14, write 4 carry 1. Add tens: 5 + 7 + 1 = 13, write 3 carry 1. Add hundreds: 3 + 4 + 1 = 8.
6. 950 - 674 = 276.
950 - 674 = 276. Subtract ones: 10 - 4 = 6 (borrow from tens). Subtract tens: 4 - 7 requires borrowing: 14 - 7 = 7. Subtract hundreds: 8 - 6 = 2.
7. 184 + 639 = 823.
184 + 639 = 823. Add ones: 4 + 9 = 13, write 3 carry 1. Add tens: 8 + 3 + 1 = 12, write 2 carry 1. Add hundreds: 1 + 6 + 1 = 8.
8. A farmer picks 712 apples and sells 385. How many are left? 327.
712 - 385 = 327. Subtract ones: 12 - 5 = 7 (borrow from tens). Subtract tens: 0 - 8 requires borrowing: 10 - 8 = 2. Subtract hundreds: 6 - 3 = 3.
9. 467 + 258 = 725.
467 + 258 = 725. Add ones: 7 + 8 = 15, write 5 carry 1. Add tens: 6 + 5 + 1 = 12, write 2 carry 1. Add hundreds: 4 + 2 + 1 = 7.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
538 + 274
→ 812
912
763 - 489
→ 274
274
345 + 567
→ 912
357
600 - 243
→ 357
812
538 + 274 = 812, 763 - 489 = 274, 345 + 567 = 912, and 600 - 243 = 357.