Perform the following subtractions. Check your results by the corresponding additions.
(i) `6237-694`
(ii) `21205-10899`
(iii) `100000 -78987`
(iv)`1010101-656565`

Answer

Let's solve the subtraction problems step by step and check the results by performing the corresponding additions.

### (i) \( 6237 - 694 \)

1. **Align the numbers**:
```
6237
- 694
```

2. **Subtract starting from the right**:
- Units place: \( 7 - 4 = 3 \)
- Tens place: \( 3 - 9 \) (can't subtract, so we borrow from the hundreds place):
- Borrow 1 from 2 (making it 1), and add 10 to 3 (making it 13).
- Now, \( 13 - 9 = 4 \)
- Hundreds place: \( 1 - 6 \) (again, can't subtract, so we borrow from the thousands place):
- Borrow 1 from 6 (making it 5), and add 10 to 1 (making it 11).
- Now, \( 11 - 6 = 5 \)
- Thousands place: \( 5 - 0 = 5 \)

3. **Final result**:
```
6237
- 694
------
5543
```

4. **Check by addition**:
- Add the result to the subtracted number:
```
5543
+ 694
------
6237
```

### (ii) \( 21205 - 10899 \)

1. **Align the numbers**:
```
21205
- 10899
```

2. **Subtract starting from the right**:
- Units place: \( 5 - 9 \) (can't subtract, so we borrow):
- Borrow 1 from 0 (making it 9), and add 10 to 5 (making it 15).
- Now, \( 15 - 9 = 6 \)
- Tens place: \( 9 - 9 = 0 \)
- Hundreds place: \( 2 - 8 \) (can't subtract, so we borrow):
- Borrow 1 from 2 (making it 1), and add 10 to 2 (making it 12).
- Now, \( 12 - 8 = 4 \)
- Thousands place: \( 1 - 0 = 1 \)
- Ten-thousands place: \( 2 - 1 = 1 \)

3. **Final result**:
```
21205
- 10899
------
10306
```

4. **Check by addition**:
```
10306
+ 10899
------
21205
```

### (iii) \( 100000 - 78987 \)

1. **Align the numbers**:
```
100000
- 78987
```

2. **Subtract starting from the right**:
- Units place: \( 0 - 7 \) (can't subtract, so we borrow):
- Borrow 1 from 0 (making it 10), and continue borrowing from the left until we reach the first non-zero digit.
- After borrowing, we get \( 10 - 7 = 3 \)
- Tens place: \( 9 - 8 = 1 \)
- Hundreds place: \( 9 - 9 = 0 \)
- Thousands place: \( 9 - 8 = 1 \)
- Ten-thousands place: \( 0 - 7 \) (again, can't subtract, so we borrow):
- After borrowing, we get \( 10 - 7 = 3 \)
- Hundred-thousands place: \( 0 - 0 = 0 \)

3. **Final result**:
```
100000
- 78987
------
21013
```

4. **Check by addition**:
```
21013
+ 78987
------
100000
```

### (iv) \( 1010101 - 656565 \)

1. **Align the numbers**:
```
1010101
- 656565
```

2. **Subtract starting from the right**:
- Units place: \( 1 - 5 \) (can't subtract, so we borrow):
- After borrowing, we get \( 11 - 5 = 6 \)
- Tens place: \( 0 - 6 \) (can't subtract, so we borrow):
- After borrowing, we get \( 10 - 6 = 4 \)
- Hundreds place: \( 1 - 5 \) (can't subtract, so we borrow):
- After borrowing, we get \( 11 - 5 = 6 \)
- Thousands place: \( 0 - 6 \) (can't subtract, so we borrow):
- After borrowing, we get \( 10 - 6 = 4 \)
- Ten-thousands place: \( 1 - 5 \) (can't subtract, so we borrow):
- After borrowing, we get \( 11 - 5 = 6 \)
- Hundred-thousands place: \( 0 - 6 \) (can't subtract, so we borrow):
- After borrowing, we get \( 10 - 6 = 4 \)

3. **Final result**:
```
1010101
- 656565
------
353536
```

4. **Check by addition**:
```
353536
+ 656565
------
1010101
```

### Summary of Results:
- (i) \( 6237 - 694 = 5543 \)
- (ii) \( 21205 - 10899 = 10306 \)
- (iii) \( 100000 - 78987 = 21013 \)
- (iv) \( 1010101 - 656565 = 353536 \)