We can subtract the 5bit binary numbers 01101_{2} (13_{10}) and 01001_{2} (9_{10}) by converting 01001_{2} to its negative equivalent in 2's complement and adding this value to 01101_{2}.

01101 (13)  01001  (9) 

01001 > 10110 

10110 + 1 10111 (9) 

01101 (13) + 10111 +(9) 100100 (?) 

01101 (13) + 10111 +(9) 00100 (4) 
Let's review the steps for subtracting x from y with an nbit 2's complement representation.
 Negate x using 2's complement.
 Reverse all the bits in x.
 Add 1 to form x.
 Add x and y.
 Discard any bits greater than n.
Now go back and compare these steps with the steps for 1's complement subtraction. Notice that with 1's complement, you must check for an overflow bit each time you perform a subtraction. If the result has an overflow, you need to add the extra bit to your result to obtain the correct answer. However, with 2's complement, we only need to ignore this extra bit. No other computations are required to find the correct answer. This makes 2's complement a more efficient way of representing signed numbers and performing binary subtraction.