Let's divide 248958 by 21
The aim is to understand the frequency of 21 in 248958.

Step 1:
If we divide 2 by 21, we get 0 and a remainder of 2.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Include the next digit (4) from the dividend after 2, then repeat: 24 / 21

Let's proceed to step 2:
If we divide 24 by 21, we get 1 and a remainder of 3.
The next digit of our result is 1. 
Result so far: 1.0
The remainder is 3 after subtracting 21 from 24.
Grab the next digit (8) from the dividend, add it to 3, then carry on: 38 / 21

Advancing to step 3:
38 divided by 21 is 1 with a remainder of 17.
The number 1 becomes the next digit in our result. 
Result so far: 11.0
If we take 21 away from 38, we end up with 17.
Grab the next digit (9) from the dividend, add it to 17, then carry on: 179 / 21

Moving on to step 4:
If we divide 179 by 21, we get 8 and a remainder of 11.
The number 8 becomes the next digit in our result. 
Result so far: 118.0
Subtract 168 from 179 to get 11.
Append the next digit (5) from the dividend to 11 and continue with: 115 / 21

Moving on to step 5:
The number 21 fits into 115 5 times, leaving a remainder of 10.
The number 5 becomes the next digit in our result. 
Result so far: 1185.0
Subtract 105 from 115 to get 10.
Append the next digit (8) from the dividend to 10 and continue with: 108 / 21

On to step 6:
21 goes into 108 5 times with a remainder of 3.
Put 5 as the next digit of the answer. 
Result so far: 11855.0
If we take 105 away from 108, we end up 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.

On to step 7:
The number 21 fits into 30 1 times, leaving a remainder of 9.
The next digit of our result is 1. 
Result so far: 11855.1
If we subtract 21 from 30, we get 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:
The number 21 fits into 90 4 times, leaving a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 11855.14
Deduct 84 from 90 and we're left with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Advancing to step 9:
21 can be fit into 60 2 times, resulting in a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 11855.142
If we take 42 away from 60, we end up with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Moving on to step 10:
When dividing 180 by 21, we get 8 with a remainder of 12.
The next digit of our result is 8. 
Result so far: 11855.1428
If we subtract 168 from 180, we get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Going ahead to step 11:
When dividing 120 by 21, we get 5 with a remainder of 15.
Use 5 as the next digit of our solution. 
Result so far: 11855.14285
Subtract 105 from 120 to get 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:
150 divided by 21 is 7 with a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 11855.142857
If we take 147 away from 150, we end up 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.

On to step 13:
21 can be fit into 30 1 times, resulting in a remainder of 9.
Put 1 as the next digit of the answer. 
Result so far: 11855.1428571
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.

Advancing to step 14:
21 goes into 90 4 times with a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 11855.14285714
Deduct 84 from 90 and we're left with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

After the division, we end up with 11855.14285714 and a remainder of 6e-09.