#Applied Course

Question

I think 3^rd option is right but they mentioned

The binary representation of -39 is : 1011001
2's complement of 1011001 will be: 1's complement of 1011001  + 1
=> 0100110 + 1 = 0100111 = 39

Comments

What is your doubt exactly?

Option $C$ is correct.

In option $B$ they used $7$ bits to represent $-39$.

Answer 1

(39)10 can be represented into 8-bit binary as 

128   64   32   16   8   4    2   1

  0      0     1     0    0    1   1    1 

                                                      (taking 1’s compliment we get)

  1      1     0     1    1    0   0    0

                                         +    1 (adding 1 to take 2’s complement)

  1      1     0     1    1    0   0    1

This matched option C and not B. In option B 7 bits are used.