20809 ÷ 2 = 10404 R1
We're going to perform division on 20809 with 2 as the divisor.

Step 1:
2 goes into 2 1 times with a remainder of 0.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 2 from 2 to get 0.
Bring next digit (0) of the dividend behind the 0 and repeat the process: 0 / 2

Step 2:
2 goes into 0 0 times with a remainder of 0.
Write down 0 as next digit of of the result. 
Result so far: 10
Subtract 0 from 0 to get 0.
Bring next digit (8) of the dividend behind the 0 and repeat the process: 8 / 2

Step 3:
2 goes into 8 4 times with a remainder of 0.
Write down 4 as next digit of of the result. 
Result so far: 104
Subtract 8 from 8 to get 0.
Bring next digit (0) of the dividend behind the 0 and repeat the process: 0 / 2

Step 4:
2 goes into 0 0 times with a remainder of 0.
Write down 0 as next digit of of the result. 
Result so far: 1040
Subtract 0 from 0 to get 0.
Bring next digit (9) of the dividend behind the 0 and repeat the process: 9 / 2

Step 5:
2 goes into 9 4 times with a remainder of 1.
Write down 4 as next digit of of the result. 
Result so far: 10404
Subtract 8 from 9 to get 1.

The final result is 10404 with a remainder of 1.