3 Digit Addition Worksheets with Answer Key - Free Printable

Problem Description:

The task involves solving a series of 3-digit addition problems. Each problem consists of two 3-digit numbers that need to be added together. The goal is to compute the sum for each pair and fill in the blanks.

Solution Approach:

We will solve each addition problem step by step, ensuring to carry over any values as needed when the sum of digits exceeds 9.

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#### Row 1:
1. 421 + 124
- Add the units place: \(1 + 4 = 5\)
- Add the tens place: \(2 + 2 = 4\)
- Add the hundreds place: \(4 + 1 = 5\)
- Result: 545

2. 381 + 202
- Add the units place: \(1 + 2 = 3\)
- Add the tens place: \(8 + 0 = 8\)
- Add the hundreds place: \(3 + 2 = 5\)
- Result: 583

3. 643 + 321
- Add the units place: \(3 + 1 = 4\)
- Add the tens place: \(4 + 2 = 6\)
- Add the hundreds place: \(6 + 3 = 9\)
- Result: 964

4. 274 + 125
- Add the units place: \(4 + 5 = 9\)
- Add the tens place: \(7 + 2 = 9\)
- Add the hundreds place: \(2 + 1 = 3\)
- Result: 399

---

#### Row 2:
5. 392 + 103
- Add the units place: \(2 + 3 = 5\)
- Add the tens place: \(9 + 0 = 9\)
- Add the hundreds place: \(3 + 1 = 4\)
- Result: 495

6. 128 + 821
- Add the units place: \(8 + 1 = 9\)
- Add the tens place: \(2 + 2 = 4\)
- Add the hundreds place: \(1 + 8 = 9\)
- Result: 949

7. 346 + 352
- Add the units place: \(6 + 2 = 8\)
- Add the tens place: \(4 + 5 = 9\)
- Add the hundreds place: \(3 + 3 = 6\)
- Result: 698

8. 638 + 222
- Add the units place: \(8 + 2 = 10\) (carry over 1)
- Add the tens place: \(3 + 2 + 1 = 6\)
- Add the hundreds place: \(6 + 2 = 8\)
- Result: 860

---

#### Row 3:
9. 821 + 177
- Add the units place: \(1 + 7 = 8\)
- Add the tens place: \(2 + 7 = 9\)
- Add the hundreds place: \(8 + 1 = 9\)
- Result: 998

10. 155 + 238
- Add the units place: \(5 + 8 = 13\) (carry over 1)
- Add the tens place: \(5 + 3 + 1 = 9\)
- Add the hundreds place: \(1 + 2 = 3\)
- Result: 393

11. 447 + 227
- Add the units place: \(7 + 7 = 14\) (carry over 1)
- Add the tens place: \(4 + 2 + 1 = 7\)
- Add the hundreds place: \(4 + 2 = 6\)
- Result: 674

12. 226 + 262
- Add the units place: \(6 + 2 = 8\)
- Add the tens place: \(2 + 6 = 8\)
- Add the hundreds place: \(2 + 2 = 4\)
- Result: 488

---

#### Row 4:
13. 724 + 137
- Add the units place: \(4 + 7 = 11\) (carry over 1)
- Add the tens place: \(2 + 3 + 1 = 6\)
- Add the hundreds place: \(7 + 1 = 8\)
- Result: 861

14. 534 + 951
- Add the units place: \(4 + 1 = 5\)
- Add the tens place: \(3 + 5 = 8\)
- Add the hundreds place: \(5 + 9 = 14\) (carry over 1 to thousands place)
- Result: 1485

15. 985 + 605
- Add the units place: \(5 + 5 = 10\) (carry over 1)
- Add the tens place: \(8 + 0 + 1 = 9\)
- Add the hundreds place: \(9 + 6 = 15\) (carry over 1 to thousands place)
- Result: 1590

16. 457 + 304
- Add the units place: \(7 + 4 = 11\) (carry over 1)
- Add the tens place: \(5 + 0 + 1 = 6\)
- Add the hundreds place: \(4 + 3 = 7\)
- Result: 761

---

Final Answers:

```
421 + 124 = 545
381 + 202 = 583
643 + 321 = 964
274 + 125 = 399

392 + 103 = 495
128 + 821 = 949
346 + 352 = 698
638 + 222 = 860

821 + 177 = 998
155 + 238 = 393
447 + 227 = 674
226 + 262 = 488

724 + 137 = 861
534 + 951 = 1485
985 + 605 = 1590
457 + 304 = 761
```

Boxed Final Answer:

\[
\boxed{
\begin{array}{cccc}
545 & 583 & 964 & 399 \\
495 & 949 & 698 & 860 \\
998 & 393 & 674 & 488 \\
861 & 1485 & 1590 & 761 \\
\end{array}
}
\]