Binary Subtraction The four possibilities for subtraction are 0–0=0 1–1=0 1–0=1 0 – 1 = 1 and adjust columns to left in the number in the top row (as illustrated below). Method: In the case of a column containing 0 – 1 put down 1 as the answer and in the top row move to the left a column at a time changing every 0 to a 1 until a 1 is found, change this 1 to a 0. Example: Calculate 1001001 – 1111. (The column being subtracted is shown as shaded.) Step 1: 1’s column-1 0 0 1 0 0 1 1 1 1 1 0Step 2: 2’s column 0 1 1 0 0 1 0 0 1 1 1 1 1< (row for adjustments to top number) 1 – 1 is 0<(row for adjustments to top number) 0 – 1 is 1, and move to left in top row and change 0 to 1 and to left again, change 1 to 0<(row for adjustments to top number) 1 -1 is 01 0 Step 3: 4’s column 0 1 1 0 1 1 0 0 1 0 0 1 1 1 1 1 0 1 0 Step 4: 8’s column 0 1 1 0 1 1 0 0 1 0 0 1 1 1 1 1 1 0 1 0 .< (row for adjustments to top number) 0 – 1 is 1, and move to left and change 0 to 1, move to left again, and change 0 to 1, and to left again and change 1 to 0Step 5: Remaining 3 columns 0 1 1 0 1 < 1 0 0 1 0 0 1 1 1 1 1 -(row for adjustments to top number) the remaining subtractions are all – 0,.0 1 1 1 0 1 0 Drop the leading 0 (at the start of the number) to give the result as 111010 Note: I consider the above method easiest – you choose the method with which you are most comfortable.