We look at the division of 43508409 by 91 
The aim is to understand the frequency of 91 in 43508409.

Moving on to step 1:
If we divide 4 by 91, we get 0 and a remainder of 4.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 4 after subtracting 0 from 4.
Bring next digit (3) of the dividend behind the 4 and repeat the process: 43 / 91

On to step 2:
The number 91 fits into 43 0 times, leaving a remainder of 43.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 43 and we're left with 43.
Append the next digit (5) from the dividend to 43 and continue with: 435 / 91

Advancing to step 3:
91 goes into 435 4 times with a remainder of 71.
The next digit of our result is 4. 
Result so far: 4.0
If we take 364 away from 435, we end up with 71.
Bring next digit (0) of the dividend behind the 71 and repeat the process: 710 / 91

Moving on to step 4:
91 can be fit into 710 7 times, resulting in a remainder of 73.
Put 7 as the next digit of the answer. 
Result so far: 47.0
Deduct 637 from 710 and we're left with 73.
Fetch the next digit (8) from the dividend, attach it to 73 and continue: 738 / 91

Step 5:
The number 91 fits into 738 8 times, leaving a remainder of 10.
The number 8 becomes the next digit in our result. 
Result so far: 478.0
Deduct 728 from 738 and we're left with 10.
Bring next digit (4) of the dividend behind the 10 and repeat the process: 104 / 91

Let's proceed to step 6:
91 can be fit into 104 1 times, resulting in a remainder of 13.
Record the quotient 1 as the next digit in the result. 
Result so far: 4781.0
If we take 91 away from 104, we end up with 13.
Take the next digit (0) from the dividend and append it to 13, then repeat: 130 / 91

Advancing to step 7:
If we divide 130 by 91, we get 1 and a remainder of 39.
Put 1 as the next digit of the answer. 
Result so far: 47811.0
The remainder is 39 after subtracting 91 from 130.
Append the next digit (9) from the dividend to 39 and continue with: 399 / 91

On to step 8:
91 can be fit into 399 4 times, resulting in a remainder of 35.
Write down 4 as next digit of the result. 
Result so far: 478114.0
The remainder is 35 after subtracting 364 from 399.
Since there are no more digits in the dividend, we add a zero to the remainder making it 350, and continue the process.

On to step 9:
When dividing 350 by 91, we get 3 with a remainder of 77.
Use 3 as the next digit of our solution. 
Result so far: 478114.3
The remainder is 77 after subtracting 273 from 350.
Since there are no more digits in the dividend, we add a zero to the remainder making it 770, and continue the process.

Step 10:
91 goes into 770 8 times with a remainder of 42.
Use 8 as the next digit of our solution. 
Result so far: 478114.38
Subtracting 728 from 770 leaves us with 42.
Since there are no more digits in the dividend, we add a zero to the remainder making it 420, and continue the process.

Let's proceed to step 11:
91 goes into 420 4 times with a remainder of 56.
The number 4 becomes the next digit in our result. 
Result so far: 478114.384
Subtracting 364 from 420 leaves us with 56.
Since there are no more digits in the dividend, we add a zero to the remainder making it 560, and continue the process.

Going ahead to step 12:
If we divide 560 by 91, we get 6 and a remainder of 14.
Put 6 as the next digit of the answer. 
Result so far: 478114.3846
Deduct 546 from 560 and we're left with 14.
Since there are no more digits in the dividend, we add a zero to the remainder making it 140, and continue the process.

Let's proceed to step 13:
91 can be fit into 140 1 times, resulting in a remainder of 49.
Put 1 as the next digit of the answer. 
Result so far: 478114.38461
If we subtract 91 from 140, we get 49.
Since there are no more digits in the dividend, we add a zero to the remainder making it 490, and continue the process.

Moving on to step 14:
The number 91 fits into 490 5 times, leaving a remainder of 35.
The next digit of our result is 5. 
Result so far: 478114.384615
Subtract 455 from 490 to get 35.
Since there are no more digits in the dividend, we add a zero to the remainder making it 350, and continue the process.

Moving on to step 15:
If we divide 350 by 91, we get 3 and a remainder of 77.
Write down 3 as next digit of the result. 
Result so far: 478114.3846153
If we take 273 away from 350, we end up with 77.
Since there are no more digits in the dividend, we add a zero to the remainder making it 770, and continue the process.

On to step 16:
91 can be fit into 770 8 times, resulting in a remainder of 42.
Put 8 as the next digit of the answer. 
Result so far: 478114.38461538
The remainder is 42 after subtracting 728 from 770.
Since there are no more digits in the dividend, we add a zero to the remainder making it 420, and continue the process.

Our division results in 478114.38461538 with a remaining 4.2e-08.