We look at the division of 121909 by 12 
Let's see how many times 12 fits into 121909.

Step 1:
1 divided by 12 is 0 with a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 1, we end up with 1.
Bring next digit (2) of the dividend behind the 1 and repeat the process: 12 / 12

Let's proceed to step 2:
If we divide 12 by 12, we get 1 and a remainder of 0.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
If we take 12 away from 12, we end up with 0.
Include the next digit (1) from the dividend after 0, then repeat: 1 / 12

On to step 3:
The number 12 fits into 1 0 times, leaving a remainder of 1.
Put 0 as the next digit of the answer. 
Result so far: 10.0
Deduct 0 from 1 and we're left with 1.
Include the next digit (9) from the dividend after 1, then repeat: 19 / 12

Advancing to step 4:
The number 12 fits into 19 1 times, leaving a remainder of 7.
The number 1 becomes the next digit in our result. 
Result so far: 101.0
If we subtract 12 from 19, we get 7.
Grab the next digit (0) from the dividend, add it to 7, then carry on: 70 / 12

Advancing to step 5:
The number 12 fits into 70 5 times, leaving a remainder of 10.
Put 5 as the next digit of the answer. 
Result so far: 1015.0
If we take 60 away from 70, we end up with 10.
Fetch the next digit (9) from the dividend, attach it to 10 and continue: 109 / 12

Step 6:
12 can be fit into 109 9 times, resulting in a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 10159.0
If we take 108 away from 109, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Step 7:
If we divide 10 by 12, we get 0 and a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 10159.0
If we take 0 away from 10, we end up with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Step 8:
100 divided by 12 is 8 with a remainder of 4.
Use 8 as the next digit of our solution. 
Result so far: 10159.08
Subtracting 96 from 100 leaves us with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Going ahead to step 9:
40 divided by 12 is 3 with a remainder of 4.
Record the quotient 3 as the next digit in the result. 
Result so far: 10159.083
Deduct 36 from 40 and we're left with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

On to step 10:
12 goes into 40 3 times with a remainder of 4.
Write down 3 as next digit of the result. 
Result so far: 10159.0833
The remainder is 4 after subtracting 36 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

The quotient of the division is 10159.0833, and the remainder is 4e-05.