Comprehensive practice sheet featuring 20 mixed three-digit addition and subtraction problems for students to solve.

Problem: Solve the addition and subtraction problems from the worksheet.

#### Worksheet Layout:
The worksheet contains 20 problems, divided into addition and subtraction. Each problem is numbered from 1 to 20. Below is the step-by-step solution for each problem.

---

Solutions:

#### Addition Problems:
1. 896 + 787
- Add the numbers column by column:
```
896
+ 787
-----
1683
```
- Answer: 1683

5. 598 + 998
- Add the numbers column by column:
```
598
+ 998
-----
1596
```
- Answer: 1596

9. 996 - 674 (This is a subtraction problem, not addition)
- Subtract the numbers column by column:
```
996
- 674
-----
322
```
- Answer: 322

13. 178 + 444
- Add the numbers column by column:
```
178
+ 444
-----
622
```
- Answer: 622

17. 941 + 735
- Add the numbers column by column:
```
941
+ 735
-----
1676
```
- Answer: 1676

18. 396 + 854
- Add the numbers column by column:
```
396
+ 854
-----
1250
```
- Answer: 1250

19. 849 - 207 (This is a subtraction problem, not addition)
- Subtract the numbers column by column:
```
849
- 207
-----
642
```
- Answer: 642

20. 572 + 998
- Add the numbers column by column:
```
572
+ 998
-----
1570
```
- Answer: 1570

---

#### Subtraction Problems:
2. 954 - 556
- Subtract the numbers column by column:
```
954
- 556
-----
398
```
- Answer: 398

3. 653 - 378
- Subtract the numbers column by column:
```
653
- 378
-----
275
```
- Answer: 275

4. 442 - 391
- Subtract the numbers column by column:
```
442
- 391
-----
51
```
- Answer: 51

6. 835 - 368
- Subtract the numbers column by column:
```
835
- 368
-----
467
```
- Answer: 467

7. 811 - 385
- Subtract the numbers column by column:
```
811
- 385
-----
426
```
- Answer: 426

8. 795 - 217
- Subtract the numbers column by column:
```
795
- 217
-----
578
```
- Answer: 578

10. 492 + 908 (This is an addition problem, not subtraction)
- Add the numbers column by column:
```
492
+ 908
-----
1400
```
- Answer: 1400

11. 669 - 245
- Subtract the numbers column by column:
```
669
- 245
-----
424
```
- Answer: 424

12. 366 - 198
- Subtract the numbers column by column:
```
366
- 198
-----
168
```
- Answer: 168

14. 693 - 398
- Subtract the numbers column by column:
```
693
- 398
-----
295
```
- Answer: 295

15. 999 - 754
- Subtract the numbers column by column:
```
999
- 754
-----
245
```
- Answer: 245

16. 549 - 255
- Subtract the numbers column by column:
```
549
- 255
-----
294
```
- Answer: 294

---

Final Answers:

1. 1683
2. 398
3. 275
4. 51
5. 1596
6. 467
7. 426
8. 578
9. 322
10. 1400
11. 424
12. 168
13. 622
14. 295
15. 245
16. 294
17. 1676
18. 1250
19. 642
20. 1570

---

Boxed Final Answer:

\[
\boxed{
\begin{array}{cccc}
1. & 1683 & 2. & 398 \\
3. & 275 & 4. & 51 \\
5. & 1596 & 6. & 467 \\
7. & 426 & 8. & 578 \\
9. & 322 & 10. & 1400 \\
11. & 424 & 12. & 168 \\
13. & 622 & 14. & 295 \\
15. & 245 & 16. & 294 \\
17. & 1676 & 18. & 1250 \\
19. & 642 & 20. & 1570 \\
\end{array}
}
\]