99878 ÷ 21 
We want to figure out the number of times 99878 can be divided by 21.

On to step 1:
When dividing 9 by 21, we get 0 with a remainder of 9.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
The remainder is 9 after subtracting 0 from 9.
Bring next digit (9) of the dividend behind the 9 and repeat the process: 99 / 21

Let's proceed to step 2:
21 goes into 99 4 times with a remainder of 15.
Write down 4 as next digit of the result. 
Result so far: 4.0
If we subtract 84 from 99, we get 15.
Take the next digit (8) from the dividend and append it to 15, then repeat: 158 / 21

Moving on to step 3:
If we divide 158 by 21, we get 7 and a remainder of 11.
The next digit of our result is 7. 
Result so far: 47.0
If we take 147 away from 158, we end up with 11.
Take the next digit (7) from the dividend and append it to 11, then repeat: 117 / 21

Moving on to step 4:
When dividing 117 by 21, we get 5 with a remainder of 12.
Use 5 as the next digit of our solution. 
Result so far: 475.0
If we subtract 105 from 117, we get 12.
Take the next digit (8) from the dividend and append it to 12, then repeat: 128 / 21

Let's proceed to step 5:
When dividing 128 by 21, we get 6 with a remainder of 2.
Use 6 as the next digit of our solution. 
Result so far: 4756.0
If we take 126 away from 128, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Moving on to step 6:
When dividing 20 by 21, we get 0 with a remainder of 20.
Put 0 as the next digit of the answer. 
Result so far: 4756.0
Subtract 0 from 20 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Let's proceed to step 7:
If we divide 200 by 21, we get 9 and a remainder of 11.
The number 9 becomes the next digit in our result. 
Result so far: 4756.09
The remainder is 11 after subtracting 189 from 200.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Step 8:
110 divided by 21 is 5 with a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 4756.095
Subtracting 105 from 110 leaves us with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Step 9:
When dividing 50 by 21, we get 2 with a remainder of 8.
Use 2 as the next digit of our solution. 
Result so far: 4756.0952
Subtract 42 from 50 to get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Going ahead to step 10:
80 divided by 21 is 3 with a remainder of 17.
The next digit of our result is 3. 
Result so far: 4756.09523
The remainder is 17 after subtracting 63 from 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Advancing to step 11:
170 divided by 21 is 8 with a remainder of 2.
Record the quotient 8 as the next digit in the result. 
Result so far: 4756.095238
If we take 168 away from 170, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

On to step 12:
The number 21 fits into 20 0 times, leaving a remainder of 20.
Record the quotient 0 as the next digit in the result. 
Result so far: 4756.095238
Subtract 0 from 20 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Advancing to step 13:
200 divided by 21 is 9 with a remainder of 11.
Write down 9 as next digit of the result. 
Result so far: 4756.09523809
If we subtract 189 from 200, we get 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

The final outcome is 4756.09523809, with a leftover of 1.1e-08.