While brain teaser interview questions are no longer popular, some companies still use them.
Don't worry too much about them. Interviewers don't expect you to prepare for all possible questions during the interview process, especially less common or unusual questions.
This article outlines the history of brain teaser questions and why interviewers ask them and answers common brain teaser interview questions.
What are brain teasers?
Brain teasers are puzzle-like questions that challenge a candidate's problem-solving skills. They're used in job interviews to assess candidates' lateral and critical thinking skills because they can't reach solutions with conventional methods.
There are many different kinds of brain teasers. Some might require math skills, others test your close listening abilities, and others rely on creativity. A brain teaser might have an exact answer, multiple solutions, or be open-ended with no correct answer.
The history of brain teaser interview questions
Google and other top companies relied on brain teaser questions to test candidates. However, these questions have fallen out of popularity.
Laszlo Bock, former Senior Vice President of People Operations at Google, said to the New York Times:
On the hiring side, we found that brainteasers are a complete waste of time. How many golf balls can you fit into an airplane? How many gas stations in Manhattan? A complete waste of time. They don’t predict anything. They serve primarily to make the interviewer feel smart.
Instead, what works well are structured behavioral interviews, where you have a consistent rubric for how you assess people, rather than having each interviewer just make stuff up.
There are many reasons why companies have dropped brain teasers for more structured behavioral interviews, including:
- If you're known for asking brain teasers, candidates can rehearse answers
- Complex questions can discourage candidates
- People who prefer to read or look at things may struggle with verbal questions
- Brain teasers don't necessarily reveal how well a candidate will work with others or how well they can do the job
- Brain teasers can take away from quality interview time
- Not all candidates react well to brain teasers, which can ruin their interview experience and damage future recruitment efforts
While brain teaser questions are no longer popular, many companies still use them. Mainly for entry-level and junior positions that require analytic and problem-solving skills in management consulting, engineering, finance, and tech.
Why do interviewers ask brain teaser questions?
Interviewers use brain teaser questions to assess a candidate's ability to think under pressure and the steps they take to get to a final answer. These questions are commonly asked in IT or management consulting positions but are not limited to these roles.
On the surface, these questions feel unrelated to the job. However, they test several competencies, including:
- Problem-solving: Can you analyze a problem and devise a solution?
- Critical thinking: Can you see the big picture, think clearly, and evaluate options?
- Analytic skills: Can you analyze data, assess probability, and make rational calculations?
- Creativity: Do you take an innovative approach to difficult problems?
- Ability to think on your feet: Can you create structure without preparation?
- Ability to perform under pressure: Do you stay calm and collected under stress?
You won't know what question the interviewer will ask, and often these questions don't have a right answer. The interviewer is more interested in your thought process than if you got the correct answer.
How you react is as important as your actual answer. So take your time, gather your thoughts, and then work through your response.
How to answer brain teaser interview questions
The best approach to answering brain teaser questions is to:
- Familiarize yourself with the different kinds of brain teaser questions: While you can't prepare for specific brain teaser questions, you can learn how to approach the different types and practice answering them aloud. Consider asking a friend or family member to ask you brain teaser questions too.
- Take a moment to consider the answer: Don't blurt out the first thing that comes to mind. Many interviewers allow you to use a pen and paper to solve brain teasers, so keep them handy during your interview. In a pinch, use the notes app on your phone.
- Ask clarifying questions: Make sure you understand the question and what the hiring manager wants to assess. See if there is any additional information they can provide. Be prepared for the interviewer to say they can't give you any further information.
- Outline your thinking process aloud: Verbalize the steps you are taking to solve the problem and the data you would need (or the estimates and assumptions you're using). Don't panic if you can't solve it all. Emphasize your process rather than the final answer.
It's easy to become flustered by these types of questions because they seem irrelevant or difficult to solve. Take a breath and relax. Remember, the interviewer is most curious about how you approach the query rather than if you get the correct answer.
If you're stumped, ask if you can come back to the question later.
Common brain teaser questions
1. The "How many?" brain teaser
A common type of brain teaser is the "How many?":
- How many golf balls can fit in a school bus?
Other variants include:
- How many gas stations are in Manhattan?
- How many piano tuners are in New York?
- How many light bulbs are in Sydney?
These types of questions ask the candidate to think through a problem. Unless you luck out, you'll need to use estimates to come to an answer.
For example, you might start with the population numbers for the country or city, then conclude how many people have cars, pianos, etc.
Interviewers don't expect you to arrive at the exact answer. They probably don't know the answer themself, nor is there an easy way to verify the answer. The idea is to hear how you think about problems and see if you make a logical attempt to solve them.
2. Riddles
Interviewers may pose a bizarre situation and ask what you would do. The interviewer assesses your creativity and ability to think on your feet with these questions.
One famous example of this question is from Google, which asked many candidates:
"You are shrunk to the height of a nickel and thrown into a blender. Your mass is reduced so that your density is the same as usual. The blades start moving in 60 seconds. What do you do?"
At face value, this is a ridiculous question. There's no practical reason you would need to answer this to do a job. However, there is a hint in the question that tested your listening skills.
If your mass is lower but your density is the same, your muscles should maintain enough power to move a normal-sized human body. If you're as small as a nickel, you could jump out.
Don't let riddle questions throw you off if you can't come to an answer. It's one question in an interview, and many other candidates will also struggle with it. Do your best to explain your process and then answer other questions well.
3. Math brain teasers
A typical brain teaser type are questions designed to test your math skills. Hiring managers at high-frequency trading firms often use math brain teasers.
Some take the form of a story. Others involve presenting a series of numbers and asking what comes next and why.
Others focus on calculating probabilities: "I roll two fair dice, what's the probability that they sum to 4?"
If you're looking to practice these types of questions to prepare for a career in finance or technology, be sure to check out this site maintained by Stanford Ph.D. Haidong Wang.
4. "Why are manhole covers round?"
"Why are manhole covers round?" is a well-known brain teaser question that originated at Microsoft. It's since become so well known that most companies have retired it. However, it's still worth calling out.
The most common answer is: "The main reason manhole covers are round is so they won't fall into the manhole. With a round cover, no matter how you hold it, you can't shove it in. If it were square, someone could hold the cover diagonally over the hole and drop it in."
Other answers include:
- Because it makes them easier to transport
- Because it makes them cheaper to manufacture as circles have a smaller surface area than squares
- Because the round shape makes it easier to put back once taken off because there are no angles for alignment
6. Communication questions
While probability or math are the basis of most brain teaser questions, some focus on communication skills:
- How would you explain how the Internet works to a six-year-old?
- A non-English speaker needs to come over and use your washing machine while you're out – what instructions do you leave?
These questions assess if you can empathize with someone else, understand their needs, and tailor your explanation accordingly.
7. Oddball questions
Some brain teasers are plain weird:
- If you were an animal, what would you be?
- Would you rather fight a hundred duck-sized horses or one horse-sized duck?
- How would you paint New York blue?
These types of questions are more suited for the pub than a job interview, but sometimes that is the point—these test whether you're the kind of person who'll fit into the company culture.
Example answers to brain teaser questions
You have a three-gallon jug and a five-gallon jug. How can you measure out exactly four gallons of water?
I obviously can't use the four-gallon jug to measure four gallons because it would overflow.
However, I still think the first step is to fill up the three-gallon jug. Then I'd pour the three gallons into the five-gallon jug.
From there, I'd fill up the three-gallon jug again and pour it into the five-gallon jug until it's full. This would use two gallons of water from the three-gallon jug, leaving me with one gallon in the three-gallon jug.
Then, I'd pour out the five-gallon jug and then pour the one-gallon from the three-gallon jug back into the five-gallon jug. Finally, I'd fill up the three-gallon jug again and pour it into the five-gallon jug, leaving me with exactly four gallons of water.
You have three boxes. One contains bananas, another apples, and a third includes both. The boxes are incorrectly labeled. You can reach into one of the boxes and pick out a piece of fruit without looking. Then you have to label the boxes correctly. How?
If each box has the wrong label, I'll start with the box labeled apples and bananas. I know that there can only be one kind of fruit in that box because the label is wrong.
Say I pick out an apple. I can then move the apple label to that box, so it's marked correctly. Then I know the banana box is labeled wrong, and it doesn't only contain bananas.
That leaves the option that box label bananas contains bananas and apples.
You're in a room with three light switches. There are three light bulbs in a neighboring room, each controlled by one of the switches. You need to figure out which switch controls each bulb, but you're only allowed to go into the room once, and you can't see from one room to the other. What do you do?
I'd label the switches 1, 2, and 3.
Then I'd turn on switch 2 for 10 minutes, turn it off, and immediately turn on switch 3.
Next, I'd go into the room to inspect the bulbs. The bulb that is off but still warm is controlled by switch 2. The bulb that is on is controlled by switch three, and the final bulb is controlled by switch 1.
I think it's essential for me to flag that my answer assumes the bulbs get hot when turned on too.
Possible follow-up questions
- Describe your work ethic
- Where do you see yourself in 5 years?
- Why did you leave your last job?
- Why do you want to work here?
- Why are you the best person for this job?
- Tell me about a time you made a mistake
- What can you bring to the company?
- Why do you deserve this job?
- Do you have any questions for me? Read our guide on the best questions to ask in an interview.
- What is your greatest weakness?
- Behavioral interview questions. Be sure to use the STAR method when answering.
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