51023780 divided by 399 
The aim is to understand the frequency of 399 in 51023780.

Step 1:
399 can be fit into 5 0 times, resulting in a remainder of 5.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 5 and we're left with 5.
Take the next digit (1) from the dividend and append it to 5, then repeat: 51 / 399

Going ahead to step 2:
When dividing 51 by 399, we get 0 with a remainder of 51.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtracting 0 from 51 leaves us with 51.
Fetch the next digit (0) from the dividend, attach it to 51 and continue: 510 / 399

Going ahead to step 3:
399 can be fit into 510 1 times, resulting in a remainder of 111.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Deduct 399 from 510 and we're left with 111.
Fetch the next digit (2) from the dividend, attach it to 111 and continue: 1112 / 399

Going ahead to step 4:
When dividing 1112 by 399, we get 2 with a remainder of 314.
The number 2 becomes the next digit in our result. 
Result so far: 12.0
Deduct 798 from 1112 and we're left with 314.
Grab the next digit (3) from the dividend, add it to 314, then carry on: 3143 / 399

Step 5:
3143 divided by 399 is 7 with a remainder of 350.
The number 7 becomes the next digit in our result. 
Result so far: 127.0
The remainder is 350 after subtracting 2793 from 3143.
Append the next digit (7) from the dividend to 350 and continue with: 3507 / 399

Advancing to step 6:
If we divide 3507 by 399, we get 8 and a remainder of 315.
The next digit of our result is 8. 
Result so far: 1278.0
Deduct 3192 from 3507 and we're left with 315.
Take the next digit (8) from the dividend and append it to 315, then repeat: 3158 / 399

Step 7:
3158 divided by 399 is 7 with a remainder of 365.
Put 7 as the next digit of the answer. 
Result so far: 12787.0
Subtract 2793 from 3158 to get 365.
Take the next digit (0) from the dividend and append it to 365, then repeat: 3650 / 399

Advancing to step 8:
If we divide 3650 by 399, we get 9 and a remainder of 59.
The next digit of our result is 9. 
Result so far: 127879.0
If we take 3591 away from 3650, we end up with 59.
Since there are no more digits in the dividend, we add a zero to the remainder making it 590, and continue the process.

On to step 9:
The number 399 fits into 590 1 times, leaving a remainder of 191.
Write down 1 as next digit of the result. 
Result so far: 127879.1
If we take 399 away from 590, we end up with 191.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1910, and continue the process.

Going ahead to step 10:
If we divide 1910 by 399, we get 4 and a remainder of 314.
Use 4 as the next digit of our solution. 
Result so far: 127879.14
If we take 1596 away from 1910, we end up with 314.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3140, and continue the process.

Let's proceed to step 11:
399 goes into 3140 7 times with a remainder of 347.
Record the quotient 7 as the next digit in the result. 
Result so far: 127879.147
If we subtract 2793 from 3140, we get 347.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3470, and continue the process.

On to step 12:
3470 divided by 399 is 8 with a remainder of 278.
The number 8 becomes the next digit in our result. 
Result so far: 127879.1478
The remainder is 278 after subtracting 3192 from 3470.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2780, and continue the process.

Advancing to step 13:
If we divide 2780 by 399, we get 6 and a remainder of 386.
Write down 6 as next digit of the result. 
Result so far: 127879.14786
The remainder is 386 after subtracting 2394 from 2780.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3860, and continue the process.

Advancing to step 14:
If we divide 3860 by 399, we get 9 and a remainder of 269.
Write down 9 as next digit of the result. 
Result so far: 127879.147869
The remainder is 269 after subtracting 3591 from 3860.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2690, and continue the process.

Let's proceed to step 15:
2690 divided by 399 is 6 with a remainder of 296.
Write down 6 as next digit of the result. 
Result so far: 127879.1478696
Subtract 2394 from 2690 to get 296.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2960, and continue the process.

Going ahead to step 16:
When dividing 2960 by 399, we get 7 with a remainder of 167.
Use 7 as the next digit of our solution. 
Result so far: 127879.14786967
Deduct 2793 from 2960 and we're left with 167.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1670, and continue the process.

After the division, we end up with 127879.14786967 and a remainder of 1.67e-07.