negative binary subtraction using 2's complement (and 5 bit representation)












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I'm wanting to carry out the calculation of 8 - 11 (assuming that 5 bits represents a number and also using 2s complement representation), however, I can't seem to get the correct answer. This is what I have so far;



8 in binary is 01000.
11 in binary is 01101, which we invert to get -11: 10010 and then add one => 10011.



Adding these together (8 + -11) I thought resulted in 11100, however, when converting this back to decimal I can see that this isn't the (final) answer. Does anyone know where I'm going wrong?










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    0














    I'm wanting to carry out the calculation of 8 - 11 (assuming that 5 bits represents a number and also using 2s complement representation), however, I can't seem to get the correct answer. This is what I have so far;



    8 in binary is 01000.
    11 in binary is 01101, which we invert to get -11: 10010 and then add one => 10011.



    Adding these together (8 + -11) I thought resulted in 11100, however, when converting this back to decimal I can see that this isn't the (final) answer. Does anyone know where I'm going wrong?










    share|cite|improve this question

























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      0








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      0





      I'm wanting to carry out the calculation of 8 - 11 (assuming that 5 bits represents a number and also using 2s complement representation), however, I can't seem to get the correct answer. This is what I have so far;



      8 in binary is 01000.
      11 in binary is 01101, which we invert to get -11: 10010 and then add one => 10011.



      Adding these together (8 + -11) I thought resulted in 11100, however, when converting this back to decimal I can see that this isn't the (final) answer. Does anyone know where I'm going wrong?










      share|cite|improve this question













      I'm wanting to carry out the calculation of 8 - 11 (assuming that 5 bits represents a number and also using 2s complement representation), however, I can't seem to get the correct answer. This is what I have so far;



      8 in binary is 01000.
      11 in binary is 01101, which we invert to get -11: 10010 and then add one => 10011.



      Adding these together (8 + -11) I thought resulted in 11100, however, when converting this back to decimal I can see that this isn't the (final) answer. Does anyone know where I'm going wrong?







      binary






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      share|cite|improve this question











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      asked Nov 5 '17 at 19:25









      Alice S

      11




      11






















          1 Answer
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          You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$



            8 = 01000
          -11 = inv(01011)+1 = 10100+1 = 10101

          01000
          + 10101
          = 11101


          Now compute $-3$ and see that results match:



           -3 = inv(00011)+1 = 11100+1 = 11101





          share|cite|improve this answer























            Your Answer





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            1 Answer
            1






            active

            oldest

            votes








            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            0














            You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$



              8 = 01000
            -11 = inv(01011)+1 = 10100+1 = 10101

            01000
            + 10101
            = 11101


            Now compute $-3$ and see that results match:



             -3 = inv(00011)+1 = 11100+1 = 11101





            share|cite|improve this answer




























              0














              You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$



                8 = 01000
              -11 = inv(01011)+1 = 10100+1 = 10101

              01000
              + 10101
              = 11101


              Now compute $-3$ and see that results match:



               -3 = inv(00011)+1 = 11100+1 = 11101





              share|cite|improve this answer


























                0












                0








                0






                You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$



                  8 = 01000
                -11 = inv(01011)+1 = 10100+1 = 10101

                01000
                + 10101
                = 11101


                Now compute $-3$ and see that results match:



                 -3 = inv(00011)+1 = 11100+1 = 11101





                share|cite|improve this answer














                You representation of $11$ is wrong (you actually compute with $-13$), here the steps to get $8-11 = -3$



                  8 = 01000
                -11 = inv(01011)+1 = 10100+1 = 10101

                01000
                + 10101
                = 11101


                Now compute $-3$ and see that results match:



                 -3 = inv(00011)+1 = 11100+1 = 11101






                share|cite|improve this answer














                share|cite|improve this answer



                share|cite|improve this answer








                edited Nov 5 '17 at 20:37

























                answered Nov 5 '17 at 20:31









                gammatester

                16.6k21632




                16.6k21632






























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