We look at the division of 866389 by 91 
The aim is to understand the frequency of 91 in 866389.

Moving on to step 1:
The number 91 fits into 8 0 times, leaving a remainder of 8.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 8 and we're left with 8.
Fetch the next digit (6) from the dividend, attach it to 8 and continue: 86 / 91

Moving on to step 2:
91 can be fit into 86 0 times, resulting in a remainder of 86.
Write down 0 as next digit of the result. 
Result so far: 0.0
The remainder is 86 after subtracting 0 from 86.
Grab the next digit (6) from the dividend, add it to 86, then carry on: 866 / 91

Step 3:
If we divide 866 by 91, we get 9 and a remainder of 47.
Use 9 as the next digit of our solution. 
Result so far: 9.0
The remainder is 47 after subtracting 819 from 866.
Include the next digit (3) from the dividend after 47, then repeat: 473 / 91

Advancing to step 4:
The number 91 fits into 473 5 times, leaving a remainder of 18.
The number 5 becomes the next digit in our result. 
Result so far: 95.0
If we subtract 455 from 473, we get 18.
Grab the next digit (8) from the dividend, add it to 18, then carry on: 188 / 91

Let's proceed to step 5:
188 divided by 91 is 2 with a remainder of 6.
The number 2 becomes the next digit in our result. 
Result so far: 952.0
Subtracting 182 from 188 leaves us with 6.
Take the next digit (9) from the dividend and append it to 6, then repeat: 69 / 91

On to step 6:
91 goes into 69 0 times with a remainder of 69.
Put 0 as the next digit of the answer. 
Result so far: 9520.0
Deduct 0 from 69 and we're left with 69.
Since there are no more digits in the dividend, we add a zero to the remainder making it 690, and continue the process.

Step 7:
91 goes into 690 7 times with a remainder of 53.
The number 7 becomes the next digit in our result. 
Result so far: 9520.7
Deduct 637 from 690 and we're left with 53.
Since there are no more digits in the dividend, we add a zero to the remainder making it 530, and continue the process.

On to step 8:
530 divided by 91 is 5 with a remainder of 75.
Use 5 as the next digit of our solution. 
Result so far: 9520.75
If we take 455 away from 530, we end up with 75.
Since there are no more digits in the dividend, we add a zero to the remainder making it 750, and continue the process.

On to step 9:
The number 91 fits into 750 8 times, leaving a remainder of 22.
Use 8 as the next digit of our solution. 
Result so far: 9520.758
If we take 728 away from 750, we end up with 22.
Since there are no more digits in the dividend, we add a zero to the remainder making it 220, and continue the process.

Going ahead to step 10:
When dividing 220 by 91, we get 2 with a remainder of 38.
Write down 2 as next digit of the result. 
Result so far: 9520.7582
If we take 182 away from 220, we end up with 38.
Since there are no more digits in the dividend, we add a zero to the remainder making it 380, and continue the process.

Going ahead to step 11:
91 can be fit into 380 4 times, resulting in a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 9520.75824
Deduct 364 from 380 and we're left with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Moving on to step 12:
If we divide 160 by 91, we get 1 and a remainder of 69.
Put 1 as the next digit of the answer. 
Result so far: 9520.758241
If we subtract 91 from 160, we get 69.
Since there are no more digits in the dividend, we add a zero to the remainder making it 690, and continue the process.

Step 13:
The number 91 fits into 690 7 times, leaving a remainder of 53.
Use 7 as the next digit of our solution. 
Result so far: 9520.7582417
Subtract 637 from 690 to get 53.
Since there are no more digits in the dividend, we add a zero to the remainder making it 530, and continue the process.

Step 14:
91 can be fit into 530 5 times, resulting in a remainder of 75.
Record the quotient 5 as the next digit in the result. 
Result so far: 9520.75824175
The remainder is 75 after subtracting 455 from 530.
Since there are no more digits in the dividend, we add a zero to the remainder making it 750, and continue the process.

After the division, we end up with 9520.75824175 and a remainder of 7.5e-08.