Question

Let A and B is the input of a subtractor then the output will be ___________

(a) A XOR B

(b) A AND B

(c) A OR B

(d) A EXNOR B

The question was asked in an interview for job.

This intriguing question comes from Half & Full Subtractor topic in section Arithmetic Circuits of Digital Circuits

Answer 1

Correct choice is (a) A XOR B

The explanation is: The subtractor has two outputs BORROW and DIFFERENCE. Since the difference output of a subtractor is given by AB’ + BA’ and this is the output of a XOR gate. So, the final difference output is AB’ + BA’.