We're dividing 81999 by 91 
The aim is to understand the frequency of 91 in 81999.

Step 1:
When dividing 8 by 91, we get 0 with a remainder of 8.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtracting 0 from 8 leaves us with 8.
Fetch the next digit (1) from the dividend, attach it to 8 and continue: 81 / 91

Going ahead to step 2:
81 divided by 91 is 0 with a remainder of 81.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 81, we get 81.
Fetch the next digit (9) from the dividend, attach it to 81 and continue: 819 / 91

Advancing to step 3:
The number 91 fits into 819 9 times, leaving a remainder of 0.
The number 9 becomes the next digit in our result. 
Result so far: 9.0
If we subtract 819 from 819, we get 0.
Take the next digit (9) from the dividend and append it to 0, then repeat: 9 / 91

On to step 4:
91 goes into 9 0 times with a remainder of 9.
Record the quotient 0 as the next digit in the result. 
Result so far: 90.0
Deduct 0 from 9 and we're left with 9.
Grab the next digit (9) from the dividend, add it to 9, then carry on: 99 / 91

Let's proceed to step 5:
If we divide 99 by 91, we get 1 and a remainder of 8.
The next digit of our result is 1. 
Result so far: 901.0
Subtract 91 from 99 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 6:
The number 91 fits into 80 0 times, leaving a remainder of 80.
Write down 0 as next digit of the result. 
Result so far: 901.0
If we subtract 0 from 80, we get 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 800, and continue the process.

Let's proceed to step 7:
The number 91 fits into 800 8 times, leaving a remainder of 72.
Put 8 as the next digit of the answer. 
Result so far: 901.08
Subtract 728 from 800 to get 72.
Since there are no more digits in the dividend, we add a zero to the remainder making it 720, and continue the process.

Step 8:
91 can be fit into 720 7 times, resulting in a remainder of 83.
Put 7 as the next digit of the answer. 
Result so far: 901.087
If we take 637 away from 720, we end up with 83.
Since there are no more digits in the dividend, we add a zero to the remainder making it 830, and continue the process.

Advancing to step 9:
830 divided by 91 is 9 with a remainder of 11.
The next digit of our result is 9. 
Result so far: 901.0879
Subtract 819 from 830 to 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.

Going ahead to step 10:
110 divided by 91 is 1 with a remainder of 19.
The next digit of our result is 1. 
Result so far: 901.08791
Subtracting 91 from 110 leaves us with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Advancing to step 11:
190 divided by 91 is 2 with a remainder of 8.
Record the quotient 2 as the next digit in the result. 
Result so far: 901.087912
The remainder is 8 after subtracting 182 from 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Advancing to step 12:
If we divide 80 by 91, we get 0 and a remainder of 80.
The number 0 becomes the next digit in our result. 
Result so far: 901.087912
If we subtract 0 from 80, we get 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 800, and continue the process.

Advancing to step 13:
When dividing 800 by 91, we get 8 with a remainder of 72.
Put 8 as the next digit of the answer. 
Result so far: 901.08791208
If we subtract 728 from 800, we get 72.
Since there are no more digits in the dividend, we add a zero to the remainder making it 720, and continue the process.

The final outcome is 901.08791208, with a leftover of 7.2e-08.