51384939 ÷ 420 
The aim is to understand the frequency of 420 in 51384939.

Going ahead to step 1:
420 can be fit into 5 0 times, resulting in a remainder of 5.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 5 and we're left with 5.
Grab the next digit (1) from the dividend, add it to 5, then carry on: 51 / 420

Step 2:
If we divide 51 by 420, we get 0 and a remainder of 51.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 51 and we're left with 51.
Grab the next digit (3) from the dividend, add it to 51, then carry on: 513 / 420

Advancing to step 3:
If we divide 513 by 420, we get 1 and a remainder of 93.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Subtract 420 from 513 to get 93.
Grab the next digit (8) from the dividend, add it to 93, then carry on: 938 / 420

On to step 4:
938 divided by 420 is 2 with a remainder of 98.
Write down 2 as next digit of the result. 
Result so far: 12.0
If we take 840 away from 938, we end up with 98.
Append the next digit (4) from the dividend to 98 and continue with: 984 / 420

Going ahead to step 5:
420 can be fit into 984 2 times, resulting in a remainder of 144.
Put 2 as the next digit of the answer. 
Result so far: 122.0
Deduct 840 from 984 and we're left with 144.
Append the next digit (9) from the dividend to 144 and continue with: 1449 / 420

On to step 6:
If we divide 1449 by 420, we get 3 and a remainder of 189.
Write down 3 as next digit of the result. 
Result so far: 1223.0
Subtract 1260 from 1449 to get 189.
Include the next digit (3) from the dividend after 189, then repeat: 1893 / 420

Step 7:
When dividing 1893 by 420, we get 4 with a remainder of 213.
Write down 4 as next digit of the result. 
Result so far: 12234.0
Deduct 1680 from 1893 and we're left with 213.
Bring next digit (9) of the dividend behind the 213 and repeat the process: 2139 / 420

Advancing to step 8:
When dividing 2139 by 420, we get 5 with a remainder of 39.
Write down 5 as next digit of the result. 
Result so far: 122345.0
Subtract 2100 from 2139 to get 39.
Since there are no more digits in the dividend, we add a zero to the remainder making it 390, and continue the process.

Let's proceed to step 9:
The number 420 fits into 390 0 times, leaving a remainder of 390.
The next digit of our result is 0. 
Result so far: 122345.0
The remainder is 390 after subtracting 0 from 390.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3900, and continue the process.

On to step 10:
If we divide 3900 by 420, we get 9 and a remainder of 120.
Record the quotient 9 as the next digit in the result. 
Result so far: 122345.09
Subtracting 3780 from 3900 leaves us with 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1200, and continue the process.

Moving on to step 11:
When dividing 1200 by 420, we get 2 with a remainder of 360.
The number 2 becomes the next digit in our result. 
Result so far: 122345.092
Deduct 840 from 1200 and we're left with 360.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3600, and continue the process.

Step 12:
If we divide 3600 by 420, we get 8 and a remainder of 240.
Put 8 as the next digit of the answer. 
Result so far: 122345.0928
Subtracting 3360 from 3600 leaves us with 240.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2400, and continue the process.

Advancing to step 13:
2400 divided by 420 is 5 with a remainder of 300.
Write down 5 as next digit of the result. 
Result so far: 122345.09285
Subtract 2100 from 2400 to get 300.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3000, and continue the process.

Moving on to step 14:
3000 divided by 420 is 7 with a remainder of 60.
The next digit of our result is 7. 
Result so far: 122345.092857
Deduct 2940 from 3000 and we're left with 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

On to step 15:
600 divided by 420 is 1 with a remainder of 180.
Record the quotient 1 as the next digit in the result. 
Result so far: 122345.0928571
The remainder is 180 after subtracting 420 from 600.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1800, and continue the process.

Let's proceed to step 16:
420 can be fit into 1800 4 times, resulting in a remainder of 120.
The number 4 becomes the next digit in our result. 
Result so far: 122345.09285714
Deduct 1680 from 1800 and we're left with 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1200, and continue the process.

Our division results in 122345.09285714 with a remaining 1.2e-07.