30 Common Brain Teaser Interview Questions
Brain teaser interview questions are those that are designed to try and determine how the interviewer answers complex questions under pressure. While they might seem like the best path to finding the most intelligent people for your role—it’s important to think through the repercussions of asking it.
First, a little on my own experience getting asked these style of questions
If you’re reading this, you might be an HR professional or potentially an interviewer yourself. And one thing I can say is that getting asked these types of questions seems fun and all. But it can actually leave a bad look and poor impression on the organization.
From my own experience getting asked these questions, here is what I often felt:
1. The culture was going to be bad
A culture that’s designed to test who is the smartest (usually against each other) is not a great culture. In fact, collaboration and support are usually the two keywords that come to mind when I think of a “healthy workplace.”
2. They didn’t trust my history of success
In most jobs, you’re not just applying using a resume. There’s most likely questions about previous job performance. Usually, in “tell me about a time” style questions.
Meaning, the candidate (or me in this case) already told the interviewer enough about prior successes that it should have been… well, enough!
This tells me that there’s very little trust inside the organization. And that’s not a great quality to have.
3. It’s about one type of “smart”
Yes, there are things such as “street smart.” And I believe it to be a very real thing. Most of the healthy organizations that I have been part of in the past had thought about the various types of people that they brought together and their working styles.
For example, the creative person should be paired with the analytical thinker. Rather than two creative people paired together. And they should have a business analyst that’s sitting alongside them trying to figure out what’s best for the company.
This pairing of skill types is what I believe leads to the most success. Testing someone’s critical-thinking skills under pressure doesn’t exactly suggest that the organization comprehends that.
If all of this still sounds okay to you… then, continue reading to the most common brain teaser interview questions that get asked.
Most common brain teaser interview questions that get asked
The Two Doors Problem:
You're in a room with two doors. One door leads to certain death, and the other door leads to freedom. There are two guards, one in front of each door. One always tells the truth, and the other always lies. You don't know which guard is which. You can ask one question to one guard to determine which door leads to freedom. What do you ask?
The Bridge Crossing:
Four people need to cross a rickety bridge at night. They have only one flashlight, and the bridge can only hold two people at a time. The four people all walk at different speeds: one can cross the bridge in 1 minute, another in 2 minutes, another in 5 minutes, and the slowest takes 10 minutes to cross. When two people cross the bridge together, they must go at the slower person's pace. What's the fastest time in which all four can cross?
The Missing Dollar:
Three people check into a hotel room that costs $30. They each contribute $10, handing $30 to the hotel clerk. Later, the clerk realizes there was a mistake, and the room only costs $25. The hotel clerk gives $5 to the bellboy and asks him to return it to the guests. The bellboy, however, decides to keep $2 for himself and gives $1 back to each of the three guests. Now, each guest has paid $9 (a total of $27) and the bellboy has kept $2, making a total of $29. What happened to the missing dollar?
The Riddle of the Sphinx:
You encounter two doors guarded by two sphinxes. One sphinx always tells the truth, and the other always lies, but you don't know which is which. One door leads to certain death, and the other door leads to freedom. You can ask one question to one sphinx to determine which door leads to safety. What do you ask?
The Poisoned Wine:
You have 1,000 bottles of wine, and one of them is poisoned. You have 10 rats to test which bottle is poisoned. How can you find the poisoned bottle in the minimum number of tries?
The Five Pirates:
Five pirates have 100 gold coins. They have to divide the coins among themselves. The pirates have a strict order of seniority, and the most senior pirate proposes a distribution. If at least 50% of the pirates (including the proposer) agree on the distribution, it happens. Otherwise, the proposer is thrown overboard, and the next pirate in seniority gets to propose a distribution. How should the most senior pirate distribute the gold to maximize their share?
The Lockers Puzzle:
There are 100 closed lockers in a hallway. A person walks by and opens every locker. Then, they walk by again and close every second locker (locker numbers 2, 4, 6, ...). Next, they walk by and change the state of every third locker (locker numbers 3, 6, 9, ...), opening it if it's closed and closing it if it's open. This process continues for 100 lockers. At the end, which lockers are open?
The 3 Light Bulbs:
You are in a room with three light bulbs. Outside the room, there are three switches, each connected to one of the bulbs. You cannot see inside the room from outside, and the door is closed. You can flip the switches as much as you like but can only open the door once. How do you determine which switch corresponds to which light bulb?
The Monty Hall Problem:
You are a contestant on a game show. There are three doors. Behind one door is a car, and behind the other two are goats. You choose a door, and then the host, who knows what's behind each door, opens one of the other two doors to reveal a goat. You are then given the option to switch your choice to the remaining unopened door. Should you switch, or does it not matter?
The Hat Colors:
There are 100 people in a line, each wearing a hat that is either red or blue. They can't see the color of their own hat but can see the colors of the hats of the people in front of them. Starting from the back of the line, each person must guess the color of their hat out loud. If they guess correctly, they live; if they guess incorrectly, they die. The people in the line can devise a strategy beforehand to maximize the number of people who survive. What strategy should they use?
The Fox, the Chicken, and the Bag of Grain:
You are by a river and need to transport a fox, a chicken, and a bag of grain across in a boat. The boat can only carry one item at a time. You can't leave the fox alone with the chicken because the fox will eat the chicken, and you can't leave the chicken alone with the grain because the chicken will eat the grain. How can you get all three safely to the other side?
The Weighted Die:
You have 8 identical-looking balls. One of them is slightly heavier than the others, but you don't know which one. You have a balance scale, and you can use it twice. How do you find the heavier ball?
The 12-Hour and 13-Hour Clocks:
You have two clocks, one that loses 2 minutes every hour (12-hour clock) and one that gains 1 minute every hour (13-hour clock). Both clocks show the correct time at noon. What time will they show when they are both correct again?
The Farmer's Dilemma:
A farmer needs to get a fox, a chicken, and a sack of corn across a river. He can only take one item at a time in his boat. If he leaves the fox and chicken alone on one side, the fox will eat the chicken. If he leaves the chicken and corn alone on one side, the chicken will eat the corn. How can he transport all three items across the river safely?
The Elevator Weight:
You're in a building with a 100-story elevator. You're given two eggs and told that they will break if dropped from a certain floor or higher. What is the fewest number of drops you need to find the highest floor from which an egg can be dropped without breaking?
The King's Dilemma:
You are the advisor to a king who is about to be invaded by a neighboring kingdom. You have a week to prepare, and you know that the enemy has a spy in your midst. The spy always tells the truth, but you don't know who the spy is. What one question can you ask to identify the spy and save your kingdom?
The Prisoner Hat Riddle:
There are 100 prisoners in a line, each wearing a black or white hat. They are allowed to see the hats of the prisoners in front of them but not their own hat or the hats of those behind them. Starting with the last prisoner and moving forward, each prisoner must guess the color of their own hat. If they guess correctly, they are freed; if they guess incorrectly, they are executed. The prisoners can discuss a strategy before this begins. What strategy should they use to maximize the number of prisoners who are freed?
The Crossing the Desert:
You are in the middle of a desert, and you have a camel. The camel can carry up to 1,000 bananas. You need to travel 1,000 miles to reach safety, and you have 3,000 bananas. However, you can only feed the camel one banana per mile. What's the maximum number of bananas you can get to safety?
The Four 4's Puzzle:
Using four 4s and any mathematical operations you like, can you find a way to represent each of the numbers from 1 to 100?
The Chessboard and Dominos:
You have a standard 8x8 chessboard, and two of the diagonally opposite corners are removed. Is it possible to cover the remaining squares with 31 dominos, each covering two adjacent squares? Why or why not?
The Prisoner Light Bulb Puzzle:
There are 100 prisoners in solitary cells, each with a light bulb that can be on or off. They cannot communicate with each other. The warden randomly selects one prisoner every day and takes them to a room with a light switch. The prisoner can either flip the switch or leave it as is. But they can also make the claim that all prisoners have been to the room at least once. If this claim is true, all prisoners are set free; otherwise, they are executed. What strategy can the prisoners use to ensure their eventual freedom?
The 100 Blue-Eyed People:
On an island, there are 100 people with blue eyes and 100 with brown eyes. They have a rule: if a person discovers their own eye color, they must leave the island at night. They have no mirrors, can't communicate about eye colors, and don't know how many people have each eye color. If one person on the island knows their own eye color, how long will it take for everyone to leave the island?
The 3 Ants:
Three ants are sitting at the three corners of an equilateral triangle. Each ant starts moving in a random direction. What is the probability that none of the ants collide?
The 25 Horses:
You have 25 horses and can race them in groups of 5 at a time. There are no stopwatches, and the tracks are too narrow for more than 5 horses to race at once. What is the minimum number of races you need to determine the fastest 3 horses?
The Four Jugs Puzzle:
You have four jugs with capacities of 5, 7, 9, and 11 liters. None of the jugs have any measurement markings. You need to measure out exactly 6 liters of water. How can you do it?
The Train Platform Problem:
You are at a train platform, and you see a train approaching. The train is 1 mile long, and it's traveling at 60 miles per hour. You are also standing next to a lever that can switch the track. On the current track, there are five people tied up, and they will be hit by the train if it continues on that track. On the other track, there is one person tied up. What do you do? Do you pull the lever to switch the track?
The Chessboard and Coins:
You have a standard chessboard with 64 squares. You also have 32 coins, and each coin covers exactly two squares (no overlapping). Is it possible to place the 32 coins on the chessboard in such a way that each square is covered by a coin, and no coin extends beyond the boundaries of the board?
The Burning Rope Puzzle:
You have two ropes, each of which takes exactly 60 minutes to burn from one end to the other. These ropes burn unevenly, so one half of a rope might burn in 10 minutes, while the other half takes 50 minutes. You need to measure exactly 45 minutes using these two ropes and a way to light them. How can you do it?
The Trapped in a Room Puzzle:
You are trapped in a room with two doors. One door leads to certain death, and the other door leads to freedom. There are two guards, one in front of each door. One guard always tells the truth, and the other always lies. You don't know which guard is which. You can ask one yes-or-no question to one guard to determine which door leads to freedom. What do you ask?
The Three Switches:
You are in a room with three light switches, each controlling a different light bulb in a different room. You can only leave the room once. How can you determine which switch controls each bulb?
Conclusion—brain tester interview questions
Ultimately, it’s up to you (the hiring manager) to decide whether asking these questions is the right thing to do based on the role. If you’re not sure, I’d say to take a look at the job description. If it doesn’t contain wording like, “has to deal with making fast decisions under pressure.” Or something similar to that, then I would keep these types of questions out of the process.
Remember, it’s best to ask questions that test against what the role needs. Not simply “who is the smartest person.” That’s simply not going to leave a good impression on the interviewee who leaves the sessions.
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