**Digital Circuits Questions and Answers – Half & Full Subtractor**

This set of Digital Electronics/Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Half & Full Subtractor”.

**1. Half subtractor is used to perform subtraction of ___________**

a) 2 bits

b) 3 bits

c) 4 bits

d) 5 bits

**Answer:**a

**Explanation:**Half subtractor is a combinational circuit which is used to perform subtraction of two bits, namely minuend and subtrahend and produces two outputs, borrow and difference.

**2. For subtracting 1 from 0, we use to take a _______ from neighbouring bits.**

a) Carry

b) Borrow

c) Input

d) Output

**Answer:**b

**Explanation:**For subtracting 1 from 0, we use to take a borrow from neighbouring bits because carry is taken into consideration during addition process.

**3. How many outputs are required for the implementation of a subtractor?**

a) 1

b) 2

c) 3

d) 4

**Answer:**b

**Explanation:**There are two outputs required for the implementation of a subtractor. One for the difference and another for borrow.

**4. Let the input of a subtractor is A and B then what the output will be if A = B?**

a) 0

b) 1

c) A

d) B

**Answer:**a

**Explanation:**The output for A = B will be 0. If A = B, it means that A = B = 0 or A = B = 1. In both of the situation subtractor gives 0 as the output.

**5. 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

**Answer:**a

**Explanation:**The subtractor has two outputs BOROW 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’.

**6. Let A and B is the input of a subtractor then the borrow will be ___________**

a) A AND B’

b) A’ AND B

c) A OR B

d) A AND B

**Answer:**b

**Explanation:**The borrow of a subtractor is received through AND gate whose one input is inverted. On that basis the borrow will be (A’ AND B).

**7. What does minuend and subtrahend denotes in a subtractor?**

a) Their corresponding bits of input

b) Its outputs

c) Its inputs

d) Borrow bits

**Answer:**c

**Explanation:**Minuend and subtrahend are the two bits of input of a subtractor. If A and B are the two inputs of a subtractor then A is called minuend and B as subtrahend.

**8. Full subtractor is used to perform subtraction of ___________**

a) 2 bits

b) 3 bits

c) 4 bits

d) 8 bits

**Answer:**b

**Explanation:**Full subtractor is used to perform subtraction of 3 bits, namely minuend bit, subtrahend bit and borrow from the previous stage. However, it also produces 2 outputs BORROW and DIFFERENCE.

**9. The full subtractor can be implemented using ___________**

a) Two XOR and an OR gates

b) Two half subtractors and an OR gate

c) Two multiplexers and an AND gate

d) Two comparators and an AND gate

**Answer:**b

**Explanation:**A full subtractor has 3 input bits and two outputs bits BORROW and DIFFERENCE. The full subtractor can be implemented using two half subtractors and an OR gate.

**10. The output of a subtractor is given by (if A, B and X are the inputs).**

a) A AND B XOR X

b) A XOR B XOR X

c) A OR B NOR X

d) A NOR B XOR X

**Answer:**b

**Explanation:**The difference output of a subtractor is given by (if A, B and X are the inputs) A XOR B XOR X.

**11. The output of a full subtractor is same as ____________**

a) Half adder

b) Full adder

c) Half subtractor

d) Decoder

**Answer:** b

**Explanation:** The sum and difference output of a full adder and a full subtractor are same. If A, B and C are the input of a full adder and a full subtractor then the output will be given by (A XOR B XOR C), respectively.

**« Prev – Digital Circuits Questions and Answers – Half Adder & Full Adder**

**» Next – Digital Circuits Questions and Answers – Procedure For The Design of Combinational Circuits**