421204 ÷ 21 
We want to divide 421204 by 21.

Step 1:
4 divided by 21 is 0 with a remainder of 4.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 4, we end up with 4.
Take the next digit (2) from the dividend and append it to 4, then repeat: 42 / 21

Moving on to step 2:
If we divide 42 by 21, we get 2 and a remainder of 0.
Write down 2 as next digit of the result. 
Result so far: 2.0
Subtract 42 from 42 to get 0.
Take the next digit (1) from the dividend and append it to 0, then repeat: 1 / 21

Going ahead to step 3:
If we divide 1 by 21, we get 0 and a remainder of 1.
Put 0 as the next digit of the answer. 
Result so far: 20.0
Subtract 0 from 1 to get 1.
Include the next digit (2) from the dividend after 1, then repeat: 12 / 21

Going ahead to step 4:
21 can be fit into 12 0 times, resulting in a remainder of 12.
Record the quotient 0 as the next digit in the result. 
Result so far: 200.0
If we take 0 away from 12, we end up with 12.
Grab the next digit (0) from the dividend, add it to 12, then carry on: 120 / 21

Moving on to step 5:
120 divided by 21 is 5 with a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 2005.0
Deduct 105 from 120 and we're left with 15.
Grab the next digit (4) from the dividend, add it to 15, then carry on: 154 / 21

Advancing to step 6:
When dividing 154 by 21, we get 7 with a remainder of 7.
Put 7 as the next digit of the answer. 
Result so far: 20057.0
If we take 147 away from 154, we end up with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Advancing to step 7:
21 goes into 70 3 times with a remainder of 7.
The next digit of our result is 3. 
Result so far: 20057.3
If we take 63 away from 70, we end up with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Step 8:
When dividing 70 by 21, we get 3 with a remainder of 7.
The next digit of our result is 3. 
Result so far: 20057.33
The remainder is 7 after subtracting 63 from 70.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

The final outcome is 20057.33, with a leftover of 0.007.