Top 20 Logical Puzzles Asked in Interviews (With Solutions)
Top 20 Logical Puzzles Asked in Interviews (With Solutions)
08-15-2025, 04:45 AM
Logical puzzles are a favorite tool for interviewers to test your problem-solving ability, critical thinking, and presence of mind. They are common in placements for IT companies, consultancies, and start-ups.
Here’s a list of the Top 20 most popular logical puzzles along with their solutions to help you prepare effectively.
1. The Two Train Puzzle
Two trains start from different cities towards each other at the same time. They meet after 4 hours. The first train is twice as fast as the second. How long did each travel?
Solution: Let the slower train’s speed = x, then faster = 2x. Distance = 4x + 8x = 12x. Each train’s time = 4 hrs.
2. The 3 Switches Puzzle
You have 3 switches in one room and 3 bulbs in another. You can enter the bulb room only once. How do you find which switch controls which bulb?
Solution: Turn on switch 1 for a few minutes, then turn it off and switch on switch 2. Enter the room — the lit bulb is switch 2, the warm bulb is switch 1, the cold one is switch 3.
3. The 100 Prisoners and Light Bulb Puzzle
Solution: One prisoner is the counter, others turn off the light only once. When the counter reaches 99, he announces all have visited.
4. The Weighing 9 Balls Puzzle
You have 9 balls, one of which is heavier. Using a balance scale, find the heavier ball in 2 weighings.
Solution: Weigh 3 vs 3, then take the heavier group and weigh 1 vs 1.
5. The Bridge and Torch Problem
4 people must cross a bridge at night with one torch. They take 1, 2, 7, and 10 minutes respectively. Only 2 can cross at a time.
Solution: Total minimum time = 17 minutes using optimal strategy.
6. The 3 Jugs Problem
You have 3 jugs with capacities 8L, 5L, and 3L. Measure exactly 4L.
Solution: Fill 5L → pour into 3L → 2L remains → empty 3L → pour 2L into 3L → fill 5L → pour into 3L.
7. The Missing Dollar Puzzle
3 people pay ₹30 for a room. The hotel returns ₹5, and the bellboy keeps ₹2. Where is the missing ₹1?
Solution: There’s no missing ₹1 — it’s a misdirection puzzle.
8. The 8 Queens Problem
Place 8 queens on a chessboard so none attack each other.
Solution: Use backtracking algorithm or known solutions.
9. The Poison Wine Puzzle
1 bottle among 1000 is poisoned. You have 10 testers and 24 hours.
Solution: Use binary representation testing to find the bottle in one round.
10. The 5 Pirates and Gold Puzzle
Pirates vote on dividing 100 gold coins. The smartest one keeps majority by offering coins to just enough pirates to secure votes.
11. The Elevator Problem
Why are people going down in an elevator more than up?
Solution: Because it starts from the top floor in the morning.
12. The Farmer, Wolf, Goat, and Cabbage Puzzle
Classic river crossing puzzle — move goat first, then cabbage, then wolf.
13. The Calendar Puzzle
Find the day of the week for a given date quickly using known formulas.
14. The Truth-Teller and Liar Puzzle
You meet two people — one always lies, one always tells truth. Ask one question to find the safe path.
Solution: Ask “If I asked the other person which way is safe, what would they say?” and take the opposite.
15. The Egg Drop Puzzle
2 eggs, 100 floors — find the minimum trials to know the breaking point.
Solution: Optimal solution ≈ 14 trials.
16. The Coin Change Puzzle
Find the fewest coins to make a certain amount from given denominations using greedy or DP method.
17. The Rope Burn Puzzle
2 ropes burn in 60 mins each, but unevenly. Measure 45 mins.
Solution: Burn rope 1 from both ends and rope 2 from one end; when rope 1 finishes (30 mins), light rope 2’s other end.
18. The 4-Digit Lock Puzzle
Crack the code using clues in minimal attempts — common in reasoning rounds.
19. The Ants on a Stick Puzzle
Ants walk on a stick and turn around on collision — find max/min time to fall off.
20. The Missing Number Puzzle
Find missing number in a series using arithmetic or logical patterns.
Tips to Solve Puzzles in Interviews:
1. Stay calm and think logically.
2. Break problems into smaller parts.
3. Avoid overcomplicating.
4. Verify your answer before presenting.
5. Practice regularly to improve speed.
Conclusion
Logical puzzles aren’t just for fun — they showcase your problem-solving and analytical thinking skills. By practicing these puzzles and understanding the solutions, you’ll be ready for any tricky interview challenge.
Keywords: Logical Puzzles for Interviews, Interview Puzzle Questions, Brain Teasers with Solutions, Placement Puzzles
Top 20 Logical Puzzles Asked in Interviews (With Solutions)
Logical puzzles are a favorite tool for interviewers to test your problem-solving ability, critical thinking, and presence of mind. They are common in placements for IT companies, consultancies, and start-ups.
Here’s a list of the Top 20 most popular logical puzzles along with their solutions to help you prepare effectively.
1. The Two Train Puzzle
Two trains start from different cities towards each other at the same time. They meet after 4 hours. The first train is twice as fast as the second. How long did each travel?
Solution: Let the slower train’s speed = x, then faster = 2x. Distance = 4x + 8x = 12x. Each train’s time = 4 hrs.
2. The 3 Switches Puzzle
You have 3 switches in one room and 3 bulbs in another. You can enter the bulb room only once. How do you find which switch controls which bulb?
Solution: Turn on switch 1 for a few minutes, then turn it off and switch on switch 2. Enter the room — the lit bulb is switch 2, the warm bulb is switch 1, the cold one is switch 3.
3. The 100 Prisoners and Light Bulb Puzzle
Solution: One prisoner is the counter, others turn off the light only once. When the counter reaches 99, he announces all have visited.
4. The Weighing 9 Balls Puzzle
You have 9 balls, one of which is heavier. Using a balance scale, find the heavier ball in 2 weighings.
Solution: Weigh 3 vs 3, then take the heavier group and weigh 1 vs 1.
5. The Bridge and Torch Problem
4 people must cross a bridge at night with one torch. They take 1, 2, 7, and 10 minutes respectively. Only 2 can cross at a time.
Solution: Total minimum time = 17 minutes using optimal strategy.
6. The 3 Jugs Problem
You have 3 jugs with capacities 8L, 5L, and 3L. Measure exactly 4L.
Solution: Fill 5L → pour into 3L → 2L remains → empty 3L → pour 2L into 3L → fill 5L → pour into 3L.
7. The Missing Dollar Puzzle
3 people pay ₹30 for a room. The hotel returns ₹5, and the bellboy keeps ₹2. Where is the missing ₹1?
Solution: There’s no missing ₹1 — it’s a misdirection puzzle.
8. The 8 Queens Problem
Place 8 queens on a chessboard so none attack each other.
Solution: Use backtracking algorithm or known solutions.
9. The Poison Wine Puzzle
1 bottle among 1000 is poisoned. You have 10 testers and 24 hours.
Solution: Use binary representation testing to find the bottle in one round.
10. The 5 Pirates and Gold Puzzle
Pirates vote on dividing 100 gold coins. The smartest one keeps majority by offering coins to just enough pirates to secure votes.
11. The Elevator Problem
Why are people going down in an elevator more than up?
Solution: Because it starts from the top floor in the morning.
12. The Farmer, Wolf, Goat, and Cabbage Puzzle
Classic river crossing puzzle — move goat first, then cabbage, then wolf.
13. The Calendar Puzzle
Find the day of the week for a given date quickly using known formulas.
14. The Truth-Teller and Liar Puzzle
You meet two people — one always lies, one always tells truth. Ask one question to find the safe path.
Solution: Ask “If I asked the other person which way is safe, what would they say?” and take the opposite.
15. The Egg Drop Puzzle
2 eggs, 100 floors — find the minimum trials to know the breaking point.
Solution: Optimal solution ≈ 14 trials.
16. The Coin Change Puzzle
Find the fewest coins to make a certain amount from given denominations using greedy or DP method.
17. The Rope Burn Puzzle
2 ropes burn in 60 mins each, but unevenly. Measure 45 mins.
Solution: Burn rope 1 from both ends and rope 2 from one end; when rope 1 finishes (30 mins), light rope 2’s other end.
18. The 4-Digit Lock Puzzle
Crack the code using clues in minimal attempts — common in reasoning rounds.
19. The Ants on a Stick Puzzle
Ants walk on a stick and turn around on collision — find max/min time to fall off.
20. The Missing Number Puzzle
Find missing number in a series using arithmetic or logical patterns.
Tips to Solve Puzzles in Interviews:
1. Stay calm and think logically.
2. Break problems into smaller parts.
3. Avoid overcomplicating.
4. Verify your answer before presenting.
5. Practice regularly to improve speed.
Conclusion
Logical puzzles aren’t just for fun — they showcase your problem-solving and analytical thinking skills. By practicing these puzzles and understanding the solutions, you’ll be ready for any tricky interview challenge.
Keywords: Logical Puzzles for Interviews, Interview Puzzle Questions, Brain Teasers with Solutions, Placement Puzzles
Recently Browsing
1 Guest(s)
1 Guest(s)
Recently Browsing
1 Guest(s)
1 Guest(s)