Let's divide 487399 by 21
The aim is to understand the frequency of 21 in 487399.

Step 1:
21 goes into 4 0 times with a remainder of 4.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 4 to get 4.
Fetch the next digit (8) from the dividend, attach it to 4 and continue: 48 / 21

Advancing to step 2:
If we divide 48 by 21, we get 2 and a remainder of 6.
Write down 2 as next digit of the result. 
Result so far: 2.0
Subtracting 42 from 48 leaves us with 6.
Append the next digit (7) from the dividend to 6 and continue with: 67 / 21

On to step 3:
If we divide 67 by 21, we get 3 and a remainder of 4.
The number 3 becomes the next digit in our result. 
Result so far: 23.0
Subtracting 63 from 67 leaves us with 4.
Fetch the next digit (3) from the dividend, attach it to 4 and continue: 43 / 21

Advancing to step 4:
If we divide 43 by 21, we get 2 and a remainder of 1.
Put 2 as the next digit of the answer. 
Result so far: 232.0
Subtract 42 from 43 to get 1.
Grab the next digit (9) from the dividend, add it to 1, then carry on: 19 / 21

Moving on to step 5:
21 goes into 19 0 times with a remainder of 19.
The number 0 becomes the next digit in our result. 
Result so far: 2320.0
If we take 0 away from 19, we end up with 19.
Take the next digit (9) from the dividend and append it to 19, then repeat: 199 / 21

Advancing to step 6:
The number 21 fits into 199 9 times, leaving a remainder of 10.
The number 9 becomes the next digit in our result. 
Result so far: 23209.0
Deduct 189 from 199 and we're left with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Advancing to step 7:
The number 21 fits into 100 4 times, leaving a remainder of 16.
Write down 4 as next digit of the result. 
Result so far: 23209.4
If we take 84 away from 100, we end up 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.

On to step 8:
When dividing 160 by 21, we get 7 with a remainder of 13.
The number 7 becomes the next digit in our result. 
Result so far: 23209.47
Subtracting 147 from 160 leaves us with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 9:
When dividing 130 by 21, we get 6 with a remainder of 4.
Record the quotient 6 as the next digit in the result. 
Result so far: 23209.476
Subtract 126 from 130 to get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

On to step 10:
If we divide 40 by 21, we get 1 and a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 23209.4761
Subtracting 21 from 40 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.

Moving on to step 11:
21 goes into 190 9 times with a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 23209.47619
If we take 189 away from 190, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

On to step 12:
21 goes into 10 0 times with a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 23209.47619
If we subtract 0 from 10, we get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Step 13:
100 divided by 21 is 4 with a remainder of 16.
Put 4 as the next digit of the answer. 
Result so far: 23209.4761904
If we subtract 84 from 100, we get 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 14:
21 goes into 160 7 times with a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 23209.47619047
Deduct 147 from 160 and we're left with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

The final outcome is 23209.47619047, with a leftover of 1.3e-08.