Subtraction

Binary Subtraction

Binary subtraction uses twos's complement and binary addition. For example if a question asks for 73-62 in binary you would convert +62 to -62 using two's complement and then do 73+(-62) using binary addition.

First you would write out 73 and 62 in their respective binary forms using your preferred method and then add 0's to make them 8bit:

73= 64+0+0+8+0+0+1 = 1001001. In 8bit 01001001
62 =32+16+8+4+2+0 = 111110. In 8bit 00111110 

Then convert +62 to -62 using your preferred method (Negative Numbers):

-62 = 11000010

Then use binary addition to add 73 and -62:

  01001001 +
  11000010
=100001011

However the addition left us with a carried 1 that makes the result 9bit, as two's complement uses 8bit we simply ignore the carried one making our final answer equal 00001011.

We can check by converting to denary:

00001011 = 8+2+1=11 and 73-62=11.