Interview Questions
Interview Brainteasers
Intro
Brainteasers have the potential to stump even the best candidates. That is because it often involves a certain perspective to find the right answer, without it you can easily draw a blank. There are different types of brain teasers including riddles, lateral thinking, root cause analysis, practical questions and more. They became popular as interview questions due to the requirement of both creative thinking and a logical approach.
The good news is that the use of brainteasers as interview questions are in decline and even a previous advocate, Google, have dropped them from their question bank. The bad news is that they are still in use for many graduate employers and still have the potential to catch you out.
Although incredibly frustrating in a lot of ways, there is only a finite amount in circulation. Sometimes the names or numbers change but fundamentally they are the same. This means that if you put in the time to practice it is unlikely you'll be caught out in an interview.
Consulting and Brain Teasers
Brain teasers are less common in consulting interviews than business cases or market sizing but they are still in circulation. This is because they can be solved with an analytical approach, something the interviewers are trying to test with all of these questions.
These questions give the interviewer a chance to test:
Thought process - How do you approach a problem that is unknown and unstructured. Using structure to find an answer where possible is a major plus.
Communication – Can you discuss your thinking clearly and show the interviewer how you arrived at the answer. A consultant must be able to explain their findings and recommendations to the client in a confident and concise way.
Creative thinking – If you get stuck can you explore alternative approaches to the same question in order to reach an answer?
Brain teaser types
Logic – These questions require you to follow the necessary logical steps in order to arrive at the right answer. For example #1:
Your mother’s brother’s only brother-in-law is asleep on your couch. Who is asleep on your couch?
Breaking this question down we start with your mother, then move to her brother, who is your uncle and its his brother-in-law that is asleep on the couch.
A brother in law is someone who is married to your sister. So, we know that your mother has a brother and so the brother-in-law to your uncle is the person his sister (your mother) is married to, a.k.a your dad.
Trick wording questions – Sometimes the answer is as obvious as it seems. Take the following question:
I have three apples, you take two from me. How many do you have?
The answer is given in the question but it is easy to make the mistake of assuming that the question is asking you to do some work. Our minds try to fill in the gaps and for this question that means doing the subtraction of 2 from three and a common answer here is 1 but that isn’t what the question asked. You took two so you have two.
Mathematical – maths is a fundamental part of consulting estimations and equations, it has immense explanatory power and as a global language it is widely understood. Taking #5
My grandson is about as many days as my daughter in weeks, and my grandson is as many months as I am in years. Together we are 120 years. How old am I?
Simultaneous equations are part of school maths and they are useful here because there are three unknowns that are all related. Setting up and solving the simultaneous equation system will give the right answer. This tests your ability to recognise and organise the relevant data.
Lateral – a test of creative thinking. When the obvious answer is no longer an option can you explore alternatives easily? Take question #10:
If you were to put a coin into an empty bottle and then insert the cork into the neck. How would you remove the coin without removing the cork or breaking the bottle?
Usually a cork is taken out of a bottle but if you can’t take it out and you can’t smash the bottle then you need to identify the problem, the cork is in the way. Then you need to resolve to remove the cork and recognising that it can go both in (counterintuitive) and out will give you the answer to this question.
Most of the questions include more than one of the types listed above but recognising them within the questions will give you a good chance of drilling down to the right answer.
15 Examples
#1
Your mother’s brother’s only brother-in-law is asleep on your couch. Who is asleep on your couch?
#2
I have three apples, you take two from me. How many do you have?
#3
The day before yesterday Sam was 17. Next year she will be 20. What day is her birthday?
#4
It’s dark. You have ten grey socks and ten blue socks you want to put into pairs. All socks are exactly the same except for their colour. How many socks would you need to take to ensure you had at least one pair?
#5
My grandson is about as many days as my daughter in weeks, and my grandson is as many months as I am in years. Together we are 120 years. How old am I?
#6
Adam’s father has 4 children; Alice, Alesha, Alan. Who is the fourth?
#7
A merchant can place 8 large boxes or 10 small boxes into a carton for shipping. In one shipment, he sent a total of 96 boxes. If there are more large boxes than small boxes, how many cartons did he ship?
#8
How many times can you subtract the number 5 from 25?
#9
Two mothers and two daughters were fishing. They managed to catch one big fish, one small fish, one fat fish. Since only three fish were caught, how is it that they each took home a fish?
#10
If you were to put a coin into an empty bottle and then insert the cork into the neck. How would you remove the coin without removing the cork or breaking the bottle?
#11
What is at the beginning of eternity, the end of time, the beginning of every end, and the end of every place?
#12
How can you propel a ball in a direction, make it stop and travel in the complete opposite direction, all in a single motion?
#13
Why is it against the law for a man living in North Carolina to be buried in South Carolina?
#14
There are five oranges in a basket, how can you distribute the oranges to five different people such that one orange is still in the basket?
#15
A man builds a rectangular house. All the sides of the house have southern exposure. A bear walks past the house. What colour is the bear?
Answers
#1
Your dad. Your mother’s brother is your uncle (assuming your mother and father are married).
#2
Two, the two apples that you took from me. I am left with one.
#3
New Year’s eve, 31st December. The day before yesterday is 30th December when she was 17, yesterday was the 31st December when she turned 18, today is the 1st of January and she will be 19 this year but next year she will be 20.
#4
Three. The first will be grey or blue, the second will either give you a match or one of each colour, if so, then the third sock will give you at least one pair.
#5
72. This makes the grandson 6 and the daughter 42. It can be solved by creating the following system of equations:
Let m be my age in years. If s is my son's age in years, then my son is 52s weeks old. If g is my grandson's age in years, then my grandson is 365g days old. Thus,
365g = 52s.
Since my grandson is 12g months old,
12g = m.
Since my grandson, my son and I together are 120 years,
g + s + m = 120.
The above system of 3 equations in 3 unknowns (g, s and m) can be solved as follows.
m / 12 + 365 m / (52 x 12) + m = 120 or
52 m + 365 m + 624 m = 624 x 120 or
m = 624 x 120 / 1041 = 72.
So, I am 72 years old.
#6
Adam. Alice, Alesha and Alan are his siblings.
#7
11 cartons total 7 large boxes (7 * 8 = 56 boxes) 4 small boxes (4 10 = 40 boxes 11 total cartons and 96 boxes
#8
Once. After you subtract 5 from 25 you are left with 20.
#9
It was a granddaughter, mother and grandmother that went fishing. The mother is both a mother and a daughter thus is counted twice in the opening sentence.
#10
Push the cork into the bottle and then remove the coin.
#11
The letter e. A lateral thinking problem, the answer has nothing to do with the meanings of the words but rather the words themselves.
#12
Throw it upwards.
#13
Burying people alive is illegal.
#14
Give the last person the basket with the last orange in it.
#15
White. It is a polar bear as the house must be built on the north pole else not all sides would face south.
Practice
If you would like to keep on practising interview brain teasers then you can download our 15 free questions or purchase our full list of interview brainteasers using the links below.
