248307 ÷ 21 
The aim is to understand the frequency of 21 in 248307.

Going ahead to step 1:
When dividing 2 by 21, we get 0 with a remainder of 2.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Grab the next digit (4) from the dividend, add it to 2, then carry on: 24 / 21

Going ahead to step 2:
24 divided by 21 is 1 with a remainder of 3.
Write down 1 as next digit of the result. 
Result so far: 1.0
If we take 21 away from 24, we end up with 3.
Append the next digit (8) from the dividend to 3 and continue with: 38 / 21

Step 3:
21 goes into 38 1 times with a remainder of 17.
Write down 1 as next digit of the result. 
Result so far: 11.0
The remainder is 17 after subtracting 21 from 38.
Bring next digit (3) of the dividend behind the 17 and repeat the process: 173 / 21

Step 4:
The number 21 fits into 173 8 times, leaving a remainder of 5.
Use 8 as the next digit of our solution. 
Result so far: 118.0
Deduct 168 from 173 and we're left with 5.
Grab the next digit (0) from the dividend, add it to 5, then carry on: 50 / 21

Step 5:
21 can be fit into 50 2 times, resulting in a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 1182.0
Deduct 42 from 50 and we're left with 8.
Grab the next digit (7) from the dividend, add it to 8, then carry on: 87 / 21

On to step 6:
87 divided by 21 is 4 with a remainder of 3.
The number 4 becomes the next digit in our result. 
Result so far: 11824.0
Subtracting 84 from 87 leaves us with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Going ahead to step 7:
If we divide 30 by 21, we get 1 and a remainder of 9.
The next digit of our result is 1. 
Result so far: 11824.1
If we take 21 away from 30, we end up with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 8:
When dividing 90 by 21, we get 4 with a remainder of 6.
The next digit of our result is 4. 
Result so far: 11824.14
The remainder is 6 after subtracting 84 from 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Let's proceed to step 9:
21 can be fit into 60 2 times, resulting in a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 11824.142
If we subtract 42 from 60, we get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Step 10:
21 can be fit into 180 8 times, resulting in a remainder of 12.
Put 8 as the next digit of the answer. 
Result so far: 11824.1428
Subtracting 168 from 180 leaves us with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Step 11:
21 can be fit into 120 5 times, resulting in a remainder of 15.
Use 5 as the next digit of our solution. 
Result so far: 11824.14285
Subtracting 105 from 120 leaves us with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Step 12:
21 goes into 150 7 times with a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 11824.142857
Subtract 147 from 150 to get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Advancing to step 13:
The number 21 fits into 30 1 times, leaving a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 11824.1428571
The remainder is 9 after subtracting 21 from 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Let's proceed to step 14:
21 can be fit into 90 4 times, resulting in a remainder of 6.
The next digit of our result is 4. 
Result so far: 11824.14285714
Subtract 84 from 90 to get 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

The final result is 11824.14285714 with a remainder of 6e-09.