In ECET 2026, Computer Organization & Architecture (COA) is a core scoring area for CSE diploma students. Topics like Binary Addition and Subtraction appear regularly and can be answered quickly if your fundamentals are strong. This is one of the easiest number system operations, but tricky questions can appear if you don’t understand carry, borrow, and signed number rules. Let’s break it down simply, followed by 10 practice MCQs with answers and explanations.
📘 Concept Notes – Binary Addition & Subtraction
🧮 Binary Addition Rules:
Binary numbers have only two digits: 0 and 1. The addition follows:
| A | B | Sum | Carry |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 0 |
| 1 | 0 | 1 | 0 |
| 1 | 1 | 0 | 1 |
Example:
1011 (11 in decimal)
+ 1101 (13 in decimal)
——————
11000 (24 in decimal)➖ Binary Subtraction Rules:
| A | B | Difference | Borrow |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 1 |
| 1 | 0 | 1 | 0 |
| 1 | 1 | 0 | 0 |
Example:
1010 (10 in decimal)
- 0011 (3 in decimal)
——————
0111 (7 in decimal)🔄 Using 2’s Complement for Subtraction:
- Find 2’s complement of the number to be subtracted.
- Add it to the minuend.
- Ignore final carry (if any) in unsigned operations.
Example:
Subtract 9 (1001) from 12 (1100):
- 2’s complement of 1001 → 0110 + 1 = 0111
- Add to 1100 → 1100 + 0111 = 1 0011 (ignore carry → 0011 = 3 decimal)
💡 Key Points:
- Binary math follows same logic as decimal but with base-2 rules.
- Carry happens when sum ≥ 2; borrow when minuend < subtrahend.
- In computers, subtraction is often done via 2’s complement addition.
🔟 10 Most Expected MCQs – ECET 2026 [Binary Addition & Subtraction]
Q1. What is 1011₂ + 1101₂ in binary?
A) 10100
B) 11000
C) 11110
D) 10000
Q2. 1001₂ + 0111₂ equals:
A) 1110
B) 10000
C) 11000
D) 10110
Q3. 1010₂ – 0011₂ equals:
A) 0101
B) 0111
C) 0011
D) 1001
Q4. In binary addition, 1 + 1 equals:
A) 10
B) 01
C) 11
D) 00
Q5. Which method is most commonly used by computers for subtraction?
A) Borrow method
B) 1’s complement
C) 2’s complement
D) Direct subtraction
Q6. What is the 2’s complement of 1010₂?
A) 0110
B) 0101
C) 1010
D) 0111
Q7. Using 2’s complement, 1100₂ – 1001₂ equals:
A) 0011
B) 0100
C) 0111
D) 1000
Q8. In binary subtraction, 0 – 1 requires:
A) No borrow
B) Borrow from next higher bit
C) Convert to decimal
D) Add 1
Q9. What is 1111₂ + 0001₂?
A) 0000 with carry 1
B) 1110
C) 0001
D) 0010
Q10. In binary addition, when sum is 10₂, what is carry?
A) 0
B) 1
C) 2
D) None
✅ Answer Key Table
| Q.No | Answer |
|---|---|
| Q1 | B |
| Q2 | B |
| Q3 | B |
| Q4 | A |
| Q5 | C |
| Q6 | A |
| Q7 | A |
| Q8 | B |
| Q9 | A |
| Q10 | B |
🧠 Explanations of All Answers
- Q1 → B: 1011 + 1101 = 11000₂ (24 decimal).
- Q2 → B: 1001 (9) + 0111 (7) = 10000₂ (16 decimal).
- Q3 → B: 1010 (10) – 0011 (3) = 0111₂ (7 decimal).
- Q4 → A: 1 + 1 in binary is 10₂ (carry 1).
- Q5 → C: Computers use 2’s complement for efficient subtraction.
- Q6 → A: 2’s complement: invert bits (0101) + 1 = 0110.
- Q7 → A: 1100 – 1001 = 0011 (3 decimal) via 2’s complement.
- Q8 → B: 0 – 1 requires borrowing from higher bit.
- Q9 → A: 1111 + 0001 = 1 0000 (carry 1, result 0000).
- Q10 → B: Sum 10₂ means carry = 1.
🎯 Why This Practice Matters for ECET 2026
Binary operations are easy to master and frequently appear in COA and Digital Electronics sections of ECET. If you know the rules, these questions take less than 10 seconds each—helping you save time for tougher problems. Mastering 2’s complement method also helps in advanced computer architecture concepts.
📲 Join Our ECET Prep Community on Telegram
Get daily MCQs, topic-wise PDFs, and mock tests directly on Telegram.
👉 Join here: @LearnNewThingsHub
