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Subtraction of Binary Numbers

Now that you are familiar with the addition of binary numbers, subtraction will be easy. The following are the four rules that you must observe when subtracting:

The following example (10110₂ - 1100₂) demonstrates the four rules of binary subtraction:

Rule 4 presents a different situation because you cannot subtract 1 from 0. Since you cannot subtract 1 from 0 and have a positive difference, you must borrow the 1 from the next higher order column of the minuend. The borrow may be indicated as shown below:

Now observe the following method of borrowing across more than one column in the example, 1000₂ - 1₂:

Let's practice some subtraction by solving the following problems:

Q.15 Subtract:

Q.16 Subtract:

Q.17 Subtract:

Q.18 Subtract:

Q.19 Subtract:

Q.20 Subtract: