We look at the division of 21135225 by 1 
We're looking to find how many times 1 goes into 21135225.

Going ahead to step 1:
2 divided by 1 is 2 with a remainder of 0.
Put 2 as the next digit of the answer. 
Result so far: 2.0
Deduct 2 from 2 and we're left with 0.
Take the next digit (1) from the dividend and append it to 0, then repeat: 1 / 1

On to step 2:
When dividing 1 by 1, we get 1 with a remainder of 0.
Put 1 as the next digit of the answer. 
Result so far: 21.0
Subtracting 1 from 1 leaves us with 0.
Bring next digit (1) of the dividend behind the 0 and repeat the process: 1 / 1

Step 3:
When dividing 1 by 1, we get 1 with a remainder of 0.
Put 1 as the next digit of the answer. 
Result so far: 211.0
If we take 1 away from 1, we end up with 0.
Bring next digit (3) of the dividend behind the 0 and repeat the process: 3 / 1

Step 4:
3 divided by 1 is 3 with a remainder of 0.
The number 3 becomes the next digit in our result. 
Result so far: 2113.0
Subtract 3 from 3 to get 0.
Grab the next digit (5) from the dividend, add it to 0, then carry on: 5 / 1

On to step 5:
1 can be fit into 5 5 times, resulting in a remainder of 0.
Use 5 as the next digit of our solution. 
Result so far: 21135.0
The remainder is 0 after subtracting 5 from 5.
Include the next digit (2) from the dividend after 0, then repeat: 2 / 1

Going ahead to step 6:
The number 1 fits into 2 2 times, leaving a remainder of 0.
Record the quotient 2 as the next digit in the result. 
Result so far: 211352.0
Subtracting 2 from 2 leaves us with 0.
Take the next digit (2) from the dividend and append it to 0, then repeat: 2 / 1

Going ahead to step 7:
When dividing 2 by 1, we get 2 with a remainder of 0.
The next digit of our result is 2. 
Result so far: 2113522.0
Deduct 2 from 2 and we're left with 0.
Grab the next digit (5) from the dividend, add it to 0, then carry on: 5 / 1

Going ahead to step 8:
1 goes into 5 5 times with a remainder of 0.
Record the quotient 5 as the next digit in the result. 
Result so far: 21135225.0
Subtracting 5 from 5 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.

Step 9:
1 goes into 0 0 times with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 21135225.0
The remainder is 0 after subtracting 0 from 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Moving on to step 10:
1 can be fit into 0 0 times, resulting in a remainder of 0.
Write down 0 as next digit of the result. 
Result so far: 21135225.0
The remainder is 0 after subtracting 0 from 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Our division results in 21135225.0 with a remaining 0.0.