81721991 divided by 90 
Our goal is to divide 81721991 by 90.

Going ahead to step 1:
90 goes into 8 0 times with a remainder of 8.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 8, we end up with 8.
Include the next digit (1) from the dividend after 8, then repeat: 81 / 90

Step 2:
90 can be fit into 81 0 times, resulting in a remainder of 81.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 81 and we're left with 81.
Grab the next digit (7) from the dividend, add it to 81, then carry on: 817 / 90

Let's proceed to step 3:
When dividing 817 by 90, we get 9 with a remainder of 7.
Put 9 as the next digit of the answer. 
Result so far: 9.0
The remainder is 7 after subtracting 810 from 817.
Bring next digit (2) of the dividend behind the 7 and repeat the process: 72 / 90

Going ahead to step 4:
72 divided by 90 is 0 with a remainder of 72.
The number 0 becomes the next digit in our result. 
Result so far: 90.0
Deduct 0 from 72 and we're left with 72.
Grab the next digit (1) from the dividend, add it to 72, then carry on: 721 / 90

Moving on to step 5:
90 goes into 721 8 times with a remainder of 1.
Write down 8 as next digit of the result. 
Result so far: 908.0
Subtract 720 from 721 to get 1.
Fetch the next digit (9) from the dividend, attach it to 1 and continue: 19 / 90

Step 6:
90 goes into 19 0 times with a remainder of 19.
The next digit of our result is 0. 
Result so far: 9080.0
Deduct 0 from 19 and we're left with 19.
Fetch the next digit (9) from the dividend, attach it to 19 and continue: 199 / 90

Going ahead to step 7:
90 can be fit into 199 2 times, resulting in a remainder of 19.
Write down 2 as next digit of the result. 
Result so far: 90802.0
Deduct 180 from 199 and we're left with 19.
Fetch the next digit (1) from the dividend, attach it to 19 and continue: 191 / 90

Let's proceed to step 8:
The number 90 fits into 191 2 times, leaving a remainder of 11.
The next digit of our result is 2. 
Result so far: 908022.0
Subtracting 180 from 191 leaves us with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Going ahead to step 9:
The number 90 fits into 110 1 times, leaving a remainder of 20.
The number 1 becomes the next digit in our result. 
Result so far: 908022.1
Subtract 90 from 110 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Going ahead to step 10:
90 can be fit into 200 2 times, resulting in a remainder of 20.
The next digit of our result is 2. 
Result so far: 908022.12
Subtract 180 from 200 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Step 11:
200 divided by 90 is 2 with a remainder of 20.
Use 2 as the next digit of our solution. 
Result so far: 908022.122
If we take 180 away from 200, we end up with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

After the division, we end up with 908022.122 and a remainder of 0.002.