A good answer might be:

<0001 0110 (correct)

The number to be subtracted is negated by the usual means (reflect the bits, add one):

0001 1011 ==> 1110 0101

Then the "binary addition algorithm" is used:

11100 001
 0011 0001    ==  49d
 1110 0101    == -27d
 ---------      -----
 0001 0110        22d

Since the carry into the most significant column is the same as the carry out of that column the result is correct. (To double check, the numbers were translated into decimal representation.)

Practice Subtraction

We are getting quite a bit of use out of the "binary addition algorithm". It is used to:

  • Add integers represented in unsigned binary.
  • Add integers represented in two's complement binary.
  • Subtract integers represented in two's complement binary.

It can't be used to subtract integers represented in unsigned binary because when used to subtract it requires the two's complement of one integer. But if subtraction is being used it is likely that the best representation is two's complement.

QUESTION 30:

Subtract 0101 1001 from 0010 0101 Is the result correct or not?