Puzzles for Interviews | 5 common puzzles and how to solve them

Did you know that often, you get asked puzzles for interviews? It may sound surprising, but it is rather common among interviewers to ask you questions that are puzzles and riddles to assess your critical thinking and problem-solving abilities. Such questions are trendy in interviews for positions in the IT sector, such as software engineer, developer, programmer, etc. You may also face them in interviews for critical positions which require quick analytical thinking and decision making, including law enforcement, armed forces, and several administrative jobs.

What are puzzles for interviews?

Puzzles are logical thinking problems like brain teasers that allow the interviewer to judge your deductive reasoning skills, wit, creativity, and ability to perform in high-pressure situations. Let’s look at how you should prepare for puzzle interview questions, some common questions asked with their answers, and some tips and tricks for when you face the interviewers.

Answering puzzle interview questions

While these interview questions may seem confusing, they are often not too difficult to answer. Here are a few things you can do to help you answer puzzles for interviews-

1. Do not rush

The most basic mistake candidates make is trying to answer as quickly as possible. Try to avoid this even if you can respond quickly. Instead, take a few seconds to think about the question and understand the problem you need to solve. If you think it may take some time, ask your interviewer to give you a minute. 

2. Ask for clarification

Puzzles and riddles are designed to be challenging to understand so that they can confuse you. So before starting to solve, ensure that you understand the question thoroughly. Ask your interviewer to clarify the question if necessary. Do not worry about making a poor impression; the interviewer will instead appreciate your seriousness in attempting. 

3. Keep an open mind

Even if you are some kind of genius with puzzles, remember that there will always be that one puzzle that is more difficult than others and may require a different approach. Do not get stuck on whatever you have practiced. Try it from all angles possible, even experiment, if you must. The interviewer from these attempts will gauge your analytical thinking.

4. Explain your answer

Interviewers usually seek crisp and to-the-point answers from candidates. However, with puzzle questions, it is always a good idea to not just answer but to explain how you arrived at your conclusion. This helps the interviewer gauge your reasoning and deduction skills and your systematic approach to solving problems.

5. Always answer

With puzzle questions, your logical reasoning in the attempt to arrive at an answer is more important than the actual answer itself. Therefore, when asked for puzzles for interviews, always respond, even if you think it is wrong. Sometimes, the interviewer may even ask questions that will have wrong answers only.  

5 common puzzle interview questions

Many puzzles may be asked in an interview, and it is practically impossible to prepare for all of them. However, most of them have some common themes and solving techniques. Here are 5 of the commonest puzzles that are asked in interviews, along with their solutions, so that you are aware of how to approach solving them.

1. You are stuck in a closed room with two doors. One of them is the right exit, and the other wrong. The doors are being protected by two guards, one for each door. The correct exit door will lead to freedom while the incorrect door leads you to eternal prison. You are allowed to ask each guard one question to help you find the correct door. But there is a catch. One of the guards will always lie, and the other will alway tell the truth. You do not know which of them tells the truth & which of them lies. What question can you ask the guards to find the correct door & escape to freedom?

There are a couple of different solutions to this problem-

Sample answer 1

I shall ask both the guards the same question: “If I were to ask the other guard to point out the right door, which door would they indicate?”

Both the guards will indicate the wrong door in response. So, I will skip that one and take the other one out.

Sample answer 2

I shall ask the guards to open the doors. Since I did not open a door myself, I shall technically not have to bear its consequences. With this, I will be able to see what is beyond each door, after which I will choose the right door.

2. You have a race track with five lanes. From out of 25 horses, you have to find the 3 fastest horses. How many races will you have to conduct to find the three fastest horses?

This question tests your thinking abilities and approach. Here is how you can answer it.

Sample answer

Conduct 5 separate races with 5 horses in each race. Then, conduct a sixth race between the winners of each of the previous 5 races. The winner of this race is the first fastest horse.

After this, conduct another race between the 4 remaining horses from the sixth race. This race’s 1st and 2nd horses are the second and third fastest horses of the entire set.

3. Three ants are sitting on three corners of an equilateral triangle. All of the ants can move in a random direction only along the triangle edges. Calculate the probability of the ants not colliding along the triangle?

Sample answer

According to the given conditions, there is a 50-50 probability of the ants never meeting and a 50-50 chance that at least two do.

As a result, all the ants must travel either in a clockwise or a counter-clockwise direction, thereby reducing the initial 50% chance of them meeting to 25% since half of 50 is 25.

4. Two trains are travelling towards each other, both at the speed of 40 km/h, from a distance of 80 km. A bird flies at 100 km/h from train 1 to train 2. After reaching train 2, the bird turns and flies along the same path back to train The bird keeps flying back and forth until the trains finally collide with each other. How much distance does the bird cover in total?

Since the trains are both moving, calculating the distance will not work. This is a mathematical problem designed to test your arithmetic abilities. The solution is as follows:

Sample answer

Velocity of the trains while approaching each other = 40 km/h + 40 km/h = 80 km/h.

Time taken till collision = distance/velocity = 80 km/80 km/h = 1 hour.

Therefore, total distance travelled by bird = Speed of the bird/time to collision = 100 km/h / 1hr = 100 km.

5. You come upon 100 closed doors arranged one after another in a straight line. You decide to pass 100 times through all the doors starting from the first. On each of your passes, you open the closed doors and close the open ones. You visit the doors according to the number of the pass you are making, starting from the door of that number and subsequently the door of that number. So you visit all the doors one by one during your first pass. On your 2nd pass, you start from the second door and visit every second door, in the third round every 3rd door, every 4th door on the 4th round, and so on. After you reach the 100th door during your last 100th round, which of the doors are open and which ones are closed?

Sample answer

The solution to this lies in a simple formula. The number of the doors you visit on each pass will be the same as the divisors of the door’s number. For example, the divisors of the number 27 are 1, 3, 9, and 27. So you will visit this door on the 1st, 3rd, 9th, and 27th passes only.

Since all the doors are closed at the beginning, and you will open closed doors and close open doors each time you visit a door, you open the initially closed 27th door on the first visit, close it on the third visit, open it again on the ninth visit, and close it finally on your 27th visit.

Whether a door will remain open or closed will depend on the number of its divisors. If it has an even number of divisors, it will remain closed, and if it has an odd number of divisors, it will remain open. Only perfect square numbers have an odd number of divisors. Therefore, only the doors, which are perfect squares, will remain open, while all the rest will be closed.

Tips and tricks for preparing puzzle interviews

Now that you know how to answer puzzle questions and some of the common questions with their solutions, you are almost ready to go and face your interview. Before you go, here are a few quick tips and tricks that will help you ace your interview. 

1. Keep pen and paper handy

Puzzle questions are often long drawn and confusing, making it easy to miss out on crucial information. Always keep paper and pen close at hand so that you never miss out on any critical point.

2. Practice well

They say “practice makes perfect,” and they are correct. Read up on as many puzzle types as possible and understand how to solve them. This will not guarantee that you will be able to solve any puzzle thrown at you, but you will undoubtedly be more confident if you come across a tough one.

3. Keep calm

Interviews are high-pressure situations, and it is very easy to panic and rush into making mistakes. Always keep a calm mind and stay collected when facing puzzle questions.

What’s next?

Interviews can be challenging, but none of them are impossible with the proper practice and right tools. We hope this article has given you all of the tips. So go out there, face your interview, and land your dream job! All the best!

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Liked this Blog? Read more: Frequently asked interview questions | A guide to preparing well!

FAQs

Q1. Will puzzles always be asked in interviews?

Answer- While most interviewers don’t always ask puzzles for interviews, they are relatively common, and some interviews may even have dedicated sections to puzzle solving. It is always a good idea to be prepared for them just in case.

Q2. I am terrible with puzzles. What to do?

Answer- The first thing you must do is relax and not panic. You must remember that puzzles are asked to test your reasoning and problem-solving abilities, both of which are inherently present in human beings in varying degrees, regardless of age. Practice solving puzzles beforehand and understand the various approaches you can take to solve these. Try to think analytically and out of the box, ask the interviewers for clarification, and explain your approach whatever answer you arrive at.

Q3. Are puzzles asked in software companies?

Answer- Since problem-solving is a big part of programming, interviewers usually test all recruits to software companies for this skill with puzzle questions. So it is relatively common in software companies to ask new recruits puzzles for interviews.