15 brain teaser interview questions and answers

In this blog post, we look at 15 brain teaser interview questions and answers to discover how your candidate thinks.

Job roles that require analytical or technical skills suit being asked brain teasers during the interview.

These questions test a number of skills, including logic, maths, critical thinking, creativity and the ability to problem-solve.

Brain teasers are different to the standard interview questions. Instead, the candidate's approach to how they get their answer is more important than the answer itself. - Even if they get the answer wrong.

A candidate who answers incorrectly but shows logic and analytical thinking will be better off than a candidate who doesn’t reveal their thought process.

Introduction: Why Do You Need Brain Teaser Interview Questions?

Brain teaser interview questions are a great way to test the problem-solving skills of a candidate. They are also a great way to see how well the person can think on their feet.

They are not for everyone, but for those who want to stand out, they can be a great asset.

These questions are used in interviews to assess the skills of a candidate. They are designed to test a range of these skills including problem solving and creativity.

People who solve these brain teaser questions correctly are able to think outside the box and come up with creative solutions. They also have the ability to think analytically and solve problems quickly.

As a recruiter, you get an insight into how your candidate thinks. You’ll understand how they approach problems and what their level of creativity is like.

Brainteasers - What are they?

Brainteasers are questions or puzzles that are designed to test a person's intelligence, creativity and problem-solving skills.

The term "brain teaser" is used to describe any puzzle, question, or riddle that requires thought and concentration to solve. Brain teasers can be classified into two groups:

  • Those that appear easy but have a deceptively difficult solution.
  • Those with a difficult solution for which the difficulty is immediately apparent.

These questions are designed to test the interviewee's mental agility. They can be used as a part of an interview process or to assess their suitability for a job.

While not always easy to answer, these questions require some thinking, but there is no one answer that is always right. That's why it is important for candidates to show their thought process when answering.

Brainteasers - How should candidates answer them

Some of the most popular brain teasers that interviewers ask candidates include:

What is heavier, a kilogram of feathers or a kilogram of bricks?

How many animals of each kind did Moses take on the ark?

What would you weigh on another planet where gravity is stronger than on earth?

Brainteasers are puzzles that test your creativity and critical thinking. They are used in interviews to assess how well you can think on your feet.

Brainteasers can be tricky, but there are a few ways to prepare for them:

- Practice logic puzzles

- Read the newspaper to stay up-to-date on current events

- Play games like chess or Scrabble

The 15 Most Popular Brain Teaser Interview Questions And How To Answer Them!

There are many ways to determine whether a candidate is qualified for a position. But these tests are a great way for employers to find out how well a candidate is equipped to do their job.

The following is a list of the top 15 most popular brainteaser interview questions.

Brain Teaser Question 1.

Which of the below is the most useful in guessing the number of people working in a 30 story building?

  1.  The of cars in the car park.
  2.  Number of people eating lunch in the cafeteria.
  3.  Total number of people on the 11th floor.

Answer:

While there is no correct answer specifically, you should be looking to see how the candidate answers this question.

How do they justify selecting their answer while they eliminate others? The answer is impossible without more data. Are candidates asking if the building is in an urban or suburban area?

They can then guess how many people would take public transport and how many would drive.

Otherwise, they can take an estimate on the number of people on one floor. -Allowing them to estimate the capacity of the building.

Brain Teaser Question 2.

In annual revenue, how much does Times Square Starbucks bring in?

Answer

Again, don’t look for specific answers. You should look to identify if the candidate can make justifiable assumptions on averages. One example can be the average cost of a ticket and traffic per hour, multiplied by 24, then 365.

Brain Teaser Question 3.

At exactly noon each day a scientist puts a bacteria in a petri dish. Every minute the bacteria divides in two. When it's at 1pm, the dish is full. What was the time when the dish was half full?

Answer

This question is not a trick question and doesn’t require the candidate to find out any extra information. The answer is quite simple. If every minute the bacteria doubles, and it’s full at 1pm. It would have been half full a minute earlier at 12:59pm.

Brain Teaser Question 4.

In one year, how many potatoes does McDonald's sell (in kg) in 1 year.

Answer

For this answer, candidates don’t need to know anything about Mcdonalds' potatoes. Rather, it’s how they approach the problem you should be mindful of.

To answer the question candidates should estimate the number of McDonald's restaurants in the region. Then to estimate the number of hash brown and fries orders a day, and the number of potatoes for each order. Then they should estimate the number of potatoes in a kilo.

Brain Teaser Question 5.

You have 50 black balls and 50 white balls and 2 buckets. How can you divide the balls into each bucket to maximise the probability of selecting a black ball at random? The ball can be chosen from either bucket at random.

Answer

For candidates to successfully answer this they should say:

There is just under a 75% chance of having a black ball chosen. It would be wise to put 1 black ball in 1 of the buckets and all the 99 balls in the other bucket.

With there being a 50% chance of selecting the bucket with one ball. Then there is a 100% chance of selecting a black ball.

Then there is also a 50% chance of selecting the bucket with 99 balls. With a 49.5% chance of selecting a black ball from this bucket.

The probability of selecting a black ball is worked out as: (50% % 100%) + (50%*49.5%) = 74.7%.

 

Brain Teaser Question 6.

If a car travels a distance of 60 miles at an average speed of 30 mph. How fast would the car need to travel the same 60 mile distance home to average 60 mph over the entire trip?

Answer

This is in fact a trick question! While most answers would say 90 mph the answer is something quite different.

At an average speed of 30mph, the first leg of the trip covers 60 miles. Equalling to the car travelling for 2 hours (60/30). For the car to average 60 mph over 120 miles, it would have to travel for exactly 2 hours (120/60). Since the car has already travelled for 2 hours, it’s impossible for it to average 60mph over the entire trip

Brain Teaser Question 7.

An interviewer presents you 3 envelopes. 

1 contains a job offer, the other 2 contain rejection letters. After you select 1 envelope, the interviewer shows you the contents of 1 of the other envelopes. -Which is a rejection letter. 

You are then given the option to stick with your original envelope or swap with the other envelope. Without knowing what your original envelope contains, should you switch?

Answer

To answer this question effectively, candidates should say yes.

This is because your original choice (envelope A) had a 1/3 chance of containing the offer letter. Leaving a 2/3 chance that the offer letter was either in envelope B or C.

By sticking with envelope A, your chance still remains 1/3.

Brain Teaser Question 8.

What is the angle between the hour-hand and minute-hand of a clock at 3:15?

Answer

At a quarter past the hour, the minute hand is exactly at 3:00. But the hour-hand has moved 1/4 of the way between 3:00 and 4:00.  Therefore 1/4 times 1/12 = 1/48 of the clock.  With the clock having 360 degrees, 360/48 = 7.5 degrees.

 Brain Teaser Question 9.

You are given a 3-gallon jug and a 5-gallon jug. How do you use them to get 4 gallons of liquid?

Answer

Fill the 5-gallon jug completely.  Pour the contents of the 5-gallon jug into the 3-gallon jug, leaving 2 gallons of liquid in the 5-gallon jug.

Next, dump out the contents of the 3-gallon jug and pour the contents of the 5-gallon jug into the 3-gallon jug.  At this point, there are 2 gallons in the 3-gallon jug.

Fill up the 5-gallon jug and then pour the contents of the 5-gallon jug into the 3-gallon jug until the 3-gallon jug is full.  You will have poured 1 gallon, leaving 4 gallons in the 5-gallon jug.

Brain Teaser Question 10.

You’ve got a 10 x 10 x 10 cube made up of 1 x 1 x 1 smaller cubes. The outside of the larger cube is completely painted red. On how many of the smaller cubes is there any red paint?

Answer

To answer this, it’s easier to think of how many of the cubes aren’t painted. The large cube is made up of 1000 small cubes. Of these, 8x8x8 of the inner cubes are not painted= 512 cubes.

Therefore, 1000-512= 488 cubes that have some paint.

Brain Teaser Question 11.

How would you test a calculator?

Answer

Again, like most of these brain teasers, there is no correct answer.

For the ideal answer candidates should say, they can test the functionality of the calculator's accuracy.

They can achieve this by evaluating whether the inputs provide their expected outputs. By testing the calculator's basic system functions. Like the power button, clear, etc to determine if there are system errors before anything else.

Brain Teaser Question 12.

You walk across a bridge and you see a boat full of people. Yet there isn’t a single person on board.

How is that possible?

Answer

These questions are designed to confuse candidates, by using conflicting words to create unexplainable scenarios.

Candidates must listen carefully to the wording of the question.

The answer to this question is “because their all married!” Suggesting more meaning to the use of the word ‘single’.

Brain Teaser Question 13.

Tracy’s mother has four children. One child is named April. The second one is May. The third is June. What‘s the fourth one’s name?

Answer

This is an illusion Brain Teaser. To answer this properly candidates must not get distracted by misleading details. The answer to this question is: “Tracy”.

The question tricks you into believing the fourth child is named “July” following the very obvious pattern of April-May-June. But it very clearly states the fourth name in the question.

Brain Teaser Question 14.

You are presented with two doors – one leading to Freedom, the other to Death. Each door has a guard, with one always lying and the other always telling the truth. For both the doors and the guards, you don’t know which one is which.

With just one question/request to one of the guards, how do you find the door of Freedom?

Answer

To answer this, candidates have to think logically and ask both guards the same question. “Please show me the door the other guard would lead me to, if I asked for the door of Freedom”. Both guards will point to the door of Death, so you take the other door.

This is because the truthful guard will show you what the lying one would do. Pointing to the death door.

The untruthful guard will show you the opposite of the truthful guard, pointing to the death door.

Brain Teaser Question 15.

What does this represent: “COF FEE”?

Answer

This is a letter-trick question. Candidates should examine many aspects of the letter to discover the meaning. The answer is “coffee break”.

How beneficial is it to ask brain teaser interview questions?

According to Google’s executive Laszlo Bock, Google has abandoned their brain teaser interview questions quoting, “They don’t predict anything.”

One of the downsides of asking brainteaser interview questions is that it can sour the candidate experience. Most candidates hate these questions. The ability to identify a great answer and link it to IQ is questionable and inconsistent.

However, on the flip side, these ‘trick’ questions allow recruiters to see the desired traits and behaviours in candidates. - Providing they can successfully recognise the skills in candidates' answers.

What do you think?

Is using brainteasers an effective method of identifying the candidate's logical thinking capacity? Or is it a time-waster, harming the candidate experience and the reputation of your brand?

Let us know in the comments below we’d love to hear what you think.

For more interviewing question tips see our blog post on: Strategic interview questions to ask candidates.

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