290399 ÷ 81 
The aim is to understand the frequency of 81 in 290399.

Step 1:
If we divide 2 by 81, we get 0 and a remainder of 2.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 2 and we're left with 2.
Take the next digit (9) from the dividend and append it to 2, then repeat: 29 / 81

Let's proceed to step 2:
If we divide 29 by 81, we get 0 and a remainder of 29.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 29, we end up with 29.
Take the next digit (0) from the dividend and append it to 29, then repeat: 290 / 81

On to step 3:
When dividing 290 by 81, we get 3 with a remainder of 47.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
The remainder is 47 after subtracting 243 from 290.
Bring next digit (3) of the dividend behind the 47 and repeat the process: 473 / 81

On to step 4:
The number 81 fits into 473 5 times, leaving a remainder of 68.
Use 5 as the next digit of our solution. 
Result so far: 35.0
Subtracting 405 from 473 leaves us with 68.
Append the next digit (9) from the dividend to 68 and continue with: 689 / 81

On to step 5:
81 can be fit into 689 8 times, resulting in a remainder of 41.
The number 8 becomes the next digit in our result. 
Result so far: 358.0
Deduct 648 from 689 and we're left with 41.
Grab the next digit (9) from the dividend, add it to 41, then carry on: 419 / 81

Advancing to step 6:
If we divide 419 by 81, we get 5 and a remainder of 14.
Record the quotient 5 as the next digit in the result. 
Result so far: 3585.0
Deduct 405 from 419 and we're left with 14.
Since there are no more digits in the dividend, we add a zero to the remainder making it 140, and continue the process.

Let's proceed to step 7:
If we divide 140 by 81, we get 1 and a remainder of 59.
The next digit of our result is 1. 
Result so far: 3585.1
If we take 81 away from 140, 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.

Step 8:
81 goes into 590 7 times with a remainder of 23.
Use 7 as the next digit of our solution. 
Result so far: 3585.17
If we take 567 away from 590, we end up with 23.
Since there are no more digits in the dividend, we add a zero to the remainder making it 230, and continue the process.

Moving on to step 9:
81 goes into 230 2 times with a remainder of 68.
Put 2 as the next digit of the answer. 
Result so far: 3585.172
If we subtract 162 from 230, we get 68.
Since there are no more digits in the dividend, we add a zero to the remainder making it 680, and continue the process.

Step 10:
When dividing 680 by 81, we get 8 with a remainder of 32.
Put 8 as the next digit of the answer. 
Result so far: 3585.1728
If we take 648 away from 680, we end up with 32.
Since there are no more digits in the dividend, we add a zero to the remainder making it 320, and continue the process.

Advancing to step 11:
The number 81 fits into 320 3 times, leaving a remainder of 77.
Put 3 as the next digit of the answer. 
Result so far: 3585.17283
Deduct 243 from 320 and we're left with 77.
Since there are no more digits in the dividend, we add a zero to the remainder making it 770, and continue the process.

On to step 12:
770 divided by 81 is 9 with a remainder of 41.
The number 9 becomes the next digit in our result. 
Result so far: 3585.172839
Subtracting 729 from 770 leaves us with 41.
Since there are no more digits in the dividend, we add a zero to the remainder making it 410, and continue the process.

Step 13:
When dividing 410 by 81, we get 5 with a remainder of 5.
The number 5 becomes the next digit in our result. 
Result so far: 3585.1728395
If we take 405 away from 410, we end up with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Let's proceed to step 14:
81 goes into 50 0 times with a remainder of 50.
Put 0 as the next digit of the answer. 
Result so far: 3585.1728395
If we subtract 0 from 50, we get 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 500, and continue the process.

The final result is 3585.1728395 with a remainder of 5e-08.