Let's divide 3991 by 99
We want to divide 3991 by 99.

Moving on to step 1:
99 goes into 3 0 times with a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 3 and we're left with 3.
Fetch the next digit (9) from the dividend, attach it to 3 and continue: 39 / 99

Moving on to step 2:
99 goes into 39 0 times with a remainder of 39.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 39 after subtracting 0 from 39.
Grab the next digit (9) from the dividend, add it to 39, then carry on: 399 / 99

Going ahead to step 3:
The number 99 fits into 399 4 times, leaving a remainder of 3.
Write down 4 as next digit of the result. 
Result so far: 4.0
If we subtract 396 from 399, we get 3.
Fetch the next digit (1) from the dividend, attach it to 3 and continue: 31 / 99

Moving on to step 4:
The number 99 fits into 31 0 times, leaving a remainder of 31.
Put 0 as the next digit of the answer. 
Result so far: 40.0
The remainder is 31 after subtracting 0 from 31.
Since there are no more digits in the dividend, we add a zero to the remainder making it 310, and continue the process.

Let's proceed to step 5:
99 can be fit into 310 3 times, resulting in a remainder of 13.
Put 3 as the next digit of the answer. 
Result so far: 40.3
The remainder is 13 after subtracting 297 from 310.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Going ahead to step 6:
99 goes into 130 1 times with a remainder of 31.
The next digit of our result is 1. 
Result so far: 40.31
Subtracting 99 from 130 leaves us with 31.
Since there are no more digits in the dividend, we add a zero to the remainder making it 310, and continue the process.

On to step 7:
The number 99 fits into 310 3 times, leaving a remainder of 13.
Use 3 as the next digit of our solution. 
Result so far: 40.313
If we subtract 297 from 310, we get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

On to step 8:
99 can be fit into 130 1 times, resulting in a remainder of 31.
The next digit of our result is 1. 
Result so far: 40.3131
If we subtract 99 from 130, we get 31.
Since there are no more digits in the dividend, we add a zero to the remainder making it 310, and continue the process.

Step 9:
The number 99 fits into 310 3 times, leaving a remainder of 13.
Use 3 as the next digit of our solution. 
Result so far: 40.31313
Subtracting 297 from 310 leaves us with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

On to step 10:
99 can be fit into 130 1 times, resulting in a remainder of 31.
Put 1 as the next digit of the answer. 
Result so far: 40.313131
If we take 99 away from 130, we end up with 31.
Since there are no more digits in the dividend, we add a zero to the remainder making it 310, and continue the process.

Advancing to step 11:
310 divided by 99 is 3 with a remainder of 13.
The next digit of our result is 3. 
Result so far: 40.3131313
The remainder is 13 after subtracting 297 from 310.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

On to step 12:
The number 99 fits into 130 1 times, leaving a remainder of 31.
Record the quotient 1 as the next digit in the result. 
Result so far: 40.31313131
If we take 99 away from 130, we end up with 31.
Since there are no more digits in the dividend, we add a zero to the remainder making it 310, and continue the process.

The final outcome is 40.31313131, with a leftover of 3.1e-08.