We look at the division of 21403 by 20 
We're looking to find how many times 20 goes into 21403.

Step 1:
If we divide 2 by 20, we get 0 and a remainder of 2.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 2 to get 2.
Grab the next digit (1) from the dividend, add it to 2, then carry on: 21 / 20

Let's proceed to step 2:
The number 20 fits into 21 1 times, leaving a remainder of 1.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
Subtracting 20 from 21 leaves us with 1.
Take the next digit (4) from the dividend and append it to 1, then repeat: 14 / 20

Advancing to step 3:
14 divided by 20 is 0 with a remainder of 14.
The next digit of our result is 0. 
Result so far: 10.0
If we take 0 away from 14, we end up with 14.
Include the next digit (0) from the dividend after 14, then repeat: 140 / 20

On to step 4:
The number 20 fits into 140 7 times, leaving a remainder of 0.
Put 7 as the next digit of the answer. 
Result so far: 107.0
The remainder is 0 after subtracting 140 from 140.
Include the next digit (3) from the dividend after 0, then repeat: 3 / 20

Step 5:
The number 20 fits into 3 0 times, leaving a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 1070.0
If we take 0 away from 3, we end up with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Advancing to step 6:
20 can be fit into 30 1 times, resulting in a remainder of 10.
Write down 1 as next digit of the result. 
Result so far: 1070.1
The remainder is 10 after subtracting 20 from 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Going ahead to step 7:
100 divided by 20 is 5 with a remainder of 0.
The number 5 becomes the next digit in our result. 
Result so far: 1070.15
Subtracting 100 from 100 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 8:
0 divided by 20 is 0 with a remainder of 0.
Use 0 as the next digit of our solution. 
Result so far: 1070.15
Subtract 0 from 0 to get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Step 9:
20 goes into 0 0 times with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 1070.15
Deduct 0 from 0 and we're left with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The final result is 1070.15 with a remainder of 0.0.