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I know that these are silly questions. But, I hope you can spare a minute to entertain this silliness.

Why is it important to have a good mental math "power" when we have our calculators in our phones?

How do brain teasers help in interviews?

AND; are there any tips to approach mental math or brain teasers in a more efficient way?

I would love to hear from the experienced people here.

Generally speaking, I am a bit on the slow side. It takes me few seconds to solve a 2 digit by 2 digit problem. It would take me even longer to do the "more complex" ones. That is a problem for me.

I am practicing more and more and hoping to gain back the skills that I have long lost.

I appreciate your input and feedback.

Hello,

I know that these are silly questions. But, I hope you can spare a minute to entertain this silliness.

Why is it important to have a good mental math "power" when we have our calculators in our phones?

How do brain teasers help in interviews?

AND; are there any tips to approach mental math or brain teasers in a more efficient way?

I would love to hear from the experienced people here.

Generally speaking, I am a bit on the slow side. It takes me few seconds to solve a 2 digit by 2 digit problem. It would take me even longer to do the "more complex" ones. That is a problem for me.

I am practicing more and more and hoping to gain back the skills that I have long lost.

I agree with Vlad, brainteasers are not very common (referring to my experience, when I applied, I got 1 out of 20+ interviews). Still, answering to your question, why do they ask them?

The main reason is to understand how you structure complex problems. Brainteasers usually require a more out-to-the-box approach that is more difficult to prepare than market sizing or cases. As a consequence they let the interviewer understand some peculiar elements of the logic of the candidate even when he/she is extensively prepared on cases.

The negative side of brainteasers is that they are usually a one-dimension type of question - that is, you need one key inside only to solve it. Business cases and market sizing include instead more key elements to be analyzed and thus offer more insides on the candidate.

Mental math is a different topic. You have to know how to do mental math in your head, as you could have to do it in front of the client. You cannot have a math problem and tell the client "Please give me one second, I will calculate 67% of 67 on my phone". Part of the skills you have to show to clients is credibility, and good mental math is one of the elements that will support that.

To improve on brainteasers, the best thing would be to download a list of the most common ones and simply practice on them - you will recognize after a while there are some commonalities between them. A good idea would be to do it gradually, allocating them proportionally in the days before the interview to keep learning constant. As mentioned, they are pretty unlikely nowadays though.

To improve on the math, you can consider the following tips:

Divide complex math in smaller logical steps: if you have to compute 96*39, you can divide it in 96*40 - 96*1 = 100*40 - 4*40 - 96*1 = 4000 – 160 – 100 + 4 = 3744

Use shortcuts: the most useful to know are:

Fractions, at least 1/6, 1/7, 1/8, 1/9

Cubes, ideally until 19^2

Practice: there are several online services you can find to improve your speed; I would recommend to keep track of the performance in an excel sheet to assess whether you are improving and if not, analyze the reasons for that

Best,

Francesco

Hi Anonymous,

I agree with Vlad, brainteasers are not very common (referring to my experience, when I applied, I got 1 out of 20+ interviews). Still, answering to your question, why do they ask them?

The main reason is to understand how you structure complex problems. Brainteasers usually require a more out-to-the-box approach that is more difficult to prepare than market sizing or cases. As a consequence they let the interviewer understand some peculiar elements of the logic of the candidate even when he/she is extensively prepared on cases.

The negative side of brainteasers is that they are usually a one-dimension type of question - that is, you need one key inside only to solve it. Business cases and market sizing include instead more key elements to be analyzed and thus offer more insides on the candidate.

Mental math is a different topic. You have to know how to do mental math in your head, as you could have to do it in front of the client. You cannot have a math problem and tell the client "Please give me one second, I will calculate 67% of 67 on my phone". Part of the skills you have to show to clients is credibility, and good mental math is one of the elements that will support that.

To improve on brainteasers, the best thing would be to download a list of the most common ones and simply practice on them - you will recognize after a while there are some commonalities between them. A good idea would be to do it gradually, allocating them proportionally in the days before the interview to keep learning constant. As mentioned, they are pretty unlikely nowadays though.

To improve on the math, you can consider the following tips:

Divide complex math in smaller logical steps: if you have to compute 96*39, you can divide it in 96*40 - 96*1 = 100*40 - 4*40 - 96*1 = 4000 – 160 – 100 + 4 = 3744

Use shortcuts: the most useful to know are:

Fractions, at least 1/6, 1/7, 1/8, 1/9

Cubes, ideally until 19^2

Practice: there are several online services you can find to improve your speed; I would recommend to keep track of the performance in an excel sheet to assess whether you are improving and if not, analyze the reasons for that

Best,

Francesco

(edited)

Anonymous replied on Oct 22, 2018

On a related note:

I have always had very positive feedback from interviewers when I told them that I already knew the answer to a given brainteaser, instead of pretending to solve it right then and there.

Bonus points for honesty and backbone, I guess. :-)

On a related note:

I have always had very positive feedback from interviewers when I told them that I already knew the answer to a given brainteaser, instead of pretending to solve it right then and there.

Bonus points for honesty and backbone, I guess. :-)

Anonymous replied on Oct 22, 2018

Hi Anonymous,

good question, I have asked myself this quite often.

I think we have to view the two things separately:

Mental Math

Yes, we do have calculators on our phone. So for a precise answer, we can always refer to the powerful computing machines around us. Mental math mostly helps to get a feeling for "Wait a second, that doesn't add up" - so to identify at which point it's time to turn on the number cruncher. It's also helpful to be able to do a bit of mental math in moments when you can't easily get out your phone and do the math - while you're presenting something, or in a no-phones meeting.

But I would really be interested in seeing scientific evidence that good mental math performance is a good predictor of job performance.

Brain teasers

Brain teasers, in general, are more a test for creativity and outside of the box thinking. Of course, there are different flavours, some more math-y, some more creative. I guess they test with how many approaches to a solution you can come up with, whether you can look beyond the obvious, whether you can think on your feet, whether you can "feel" your way to a solution. This may help you during your work because if the solution to a problem were obvious, you wouldn't call the highly paid consultants, would you now?

But again, I haven't seen any scientific evidence that brain teaser chops translate into good consulting skills.

Cheers

Elias

Hi Anonymous,

good question, I have asked myself this quite often.

I think we have to view the two things separately:

Mental Math

Yes, we do have calculators on our phone. So for a precise answer, we can always refer to the powerful computing machines around us. Mental math mostly helps to get a feeling for "Wait a second, that doesn't add up" - so to identify at which point it's time to turn on the number cruncher. It's also helpful to be able to do a bit of mental math in moments when you can't easily get out your phone and do the math - while you're presenting something, or in a no-phones meeting.

But I would really be interested in seeing scientific evidence that good mental math performance is a good predictor of job performance.

Brain teasers

Brain teasers, in general, are more a test for creativity and outside of the box thinking. Of course, there are different flavours, some more math-y, some more creative. I guess they test with how many approaches to a solution you can come up with, whether you can look beyond the obvious, whether you can think on your feet, whether you can "feel" your way to a solution. This may help you during your work because if the solution to a problem were obvious, you wouldn't call the highly paid consultants, would you now?

But again, I haven't seen any scientific evidence that brain teaser chops translate into good consulting skills.

Cheers

Elias

Hi Elias. As always. Thank you for the very useful insights and commentary. —
Mike (Mustafa) on Oct 23, 2018(edited)

There is no dedicated part of the interview for brainteasers and to be honest they are quite rare. Although the interviewer might want to ask you a brainteaser question either before or after the case. To prepare you simply read the 2-3 most popular books with the brainteasers (Are you smart enough to work at Google?, How would you move Mount Fuji?).

Best

Hi,

There is no dedicated part of the interview for brainteasers and to be honest they are quite rare. Although the interviewer might want to ask you a brainteaser question either before or after the case. To prepare you simply read the 2-3 most popular books with the brainteasers (Are you smart enough to work at Google?, How would you move Mount Fuji?).

Best

HI Vlad. Thanks for the tips. An I like the one with moving Mount Fuji. Cheers. —
Mike (Mustafa) on Oct 23, 2018

Hey,
in general I believe it is not mainly about the ability to do mental math.
It is about the competences you show while doing these estimation tasks.

For example the ability to:

Think fast

Structure yourself in an understandable way

Make sound assumptions to solve your problems

Of course it is also about precision - imagine how MC Kinsey would look like in front of their customers if one of their consultants is making several math mistakes in a conversation. It all falls back to the company.

I hope it makes sense.

All the best,
Tobi

Hey,
in general I believe it is not mainly about the ability to do mental math.
It is about the competences you show while doing these estimation tasks.

For example the ability to:

Think fast

Structure yourself in an understandable way

Make sound assumptions to solve your problems

Of course it is also about precision - imagine how MC Kinsey would look like in front of their customers if one of their consultants is making several math mistakes in a conversation. It all falls back to the company.

Nearly all the math required in case interviews is arithmetic: addition, subtraction, multiplication and division. We help you do calculations with large numbers quickly and without calculators.

MBMC Case: Exploring future Business Models on Four WheelsAs a consultant at Mercedes-Benz Management Consulting, you are actively shaping the future of mobility. While you are contributing to decisive projects that design the future of the world’s No.1 premium carmaker, you also develop your own career path and you have the unique possibility to build your personal brand and cultivate relationships with the top management.
Your client on your current project, the C-Class model series responsible, asks you to explore new profit pools and business opportunities regarding optional equipment.
Initially, you shall structure and explore potential business models, and discuss necessary conditions and implications of these business models. In a next step, you shall identify possible options and prepare them for decision. And of course, the client is interested in your recommendation.

As a consultant at Mercedes-Benz Management Consulting, you are actively shaping the future of mobility. While you are contributing to decisive projects that design the future of the world’s No.1 premium carmaker, you also develop your own career path and you have the unique possibility to build you ... Open whole case

Brain Teasers - U2 ConcertNumber sequence
Situation:
“You and I will take turns saying numbers. The first person will say a number between 1 and 10. Then, the other person will say a number that is greater than the first number. The difference between both numbers must be between 1 and 10. We will keep going back and forth in this way until one of us says the number 50. That person wins. You will start.”
Question:
What number should you start with?
U2 Concert
Situation:
U2 has a concert that starts in just 17 minutes. To get there, all the band members must cross a bridge. Since the bridge is old, a maximum of two people can cross the bridge at any one time. To make matters worse, it is dark and there is only one torch. Anyone crossing the bridge must carry a torch. The torch cannot be thrown across the bridge. Instead, someone must walk it back to the other side. Each band member walks at a different speed. If two members cross at the same time, both must walk at the speed of the slower band member.
Bono takes 1 minute to cross.
Edge takes 2 minutes to cross.
Adam takes 5 minutes to cross.
Larry takes 10 minutes to cross.
Question:
Can the band make it to the concert in time? How will they manage this?
Buckets
Situation:
You have a 5-gallon bucket and a 3-gallon bucket. (Assume that you have an unlimited supply of water and that the buckets do not have any markings for measurement.
Question:
How can you get 4 gallons of water into the 5-gallon bucket?
Cigars
Situation:
A homeless man collects cigar butts. He uses 5 cigar butts to make a new cigar. Today, he has collected 25 cigar butts.
Question:
How many cigars can he smoke?

Number sequence
Situation:
“You and I will take turns saying numbers. The first person will say a number between 1 and 10. Then, the other person will say a number that is greater than the first number. The difference between both numbers must be between 1 and 10. We will keep going back and forth ... Open whole case

Brain Teasers - MotelMotel
Situation:
Three friends check into a motel for the night. The clerk tells them the bill is $30, payable in advance. They each pay the clerk $10 and go to their room. A few minutes later, the clerk realizes he has made an error and overcharged the trio by $5. He asks the bellhop to return $5 to the 3 friends who had just checked in. The bellhop sees this as an opportunity to make $2 as he reasons that the three friends would have a tough time dividing $5 evenly among them; so he decides to tell them that the clerk made a mistake of only $3, giving a dollar back to each of the friends. He pockets the leftover $2 and goes home for the day!
Question:
Now, each of the three friends gets a dollar back, thus they each paid $9 for the room which is a total of $27 for the night. We know the bellhop pocketed $2 and adding that to the $27, you get $29, not $30 that was originally spent. Where did the other dollar go?
Murder
Situation:
The midnight train is coming down the mountains. Art Farnanski seems to be sleeping in his seat. At the station, all the passengers get off the train except one. The conductor comes and taps him on the shoulder to let him know they have arrived. Art Farnanski does not answer. He is dead.
Hours later the four people that had shared the train compartment with the dead man are at the police station.
The man in the dark suit:
"I'm innocent. The blonde woman was talking to Farnanski."
The blonde woman:
"I'm innocent. I did not speak to Farnanski."
The man in the light suit:
"I'm innocent. The brunette woman killed him."
The brunette woman:
"I'm innocent. One of the men killed him."
Question:
The police detective comes up to you and says: “I know that four statements are wrong and four are true. Who killed Farnanski? (Only one person is guilty).”
Trees
Statement:
You have 10 trees and you have to plant them in five rows, but each row must contain 4 trees.
Question:
How is this possible?

Motel
Situation:
Three friends check into a motel for the night. The clerk tells them the bill is $30, payable in advance. They each pay the clerk $10 and go to their room. A few minutes later, the clerk realizes he has made an error and overcharged the trio by $5. He asks the bellhop to return $5 ... Open whole case

Brain Teasers - PiratesPirates
Situation:
Five pirates are trying to split up 1000 gold pieces. The rules are as follows:
Pirate #1 must divide the gold up in such a way that a majority of the pirates (including himself) agree to. If he does not get a majority vote, he will be killed, and pirate #2 will get to propose a solution to the remaining 3 pirates, and the same rules will follow. This continues until someone comes up with a plan that earns a majority vote.
The pirates are infinitely greedy, infinitely ruthless (the more dead pirates the better), and infinitely intelligent.
Question:
What is the highest amount of gold pieces that pirate #1 can keep and what would his proposal be?
Chicken
Situation:
A man is traveling with a fox and two chickens, if he leaves the fox alone with the chickens the fox will eat the chickens. He arrives at a river and needs to cross it. He finds a small boat that can carry only him and one animal.
Question:
How does he get himself, the fox and the two chickens across the river safely?

Pirates
Situation:
Five pirates are trying to split up 1000 gold pieces. The rules are as follows:
Pirate #1 must divide the gold up in such a way that a majority of the pirates (including himself) agree to. If he does not get a majority vote, he will be killed, and pirate #2 will get to propose ... Open whole case

Brain Teasers - FirefighterFirefighter
Situation:
A firefighter stood on the middle rung of a ladder, spraying water on a burning house. He then climbed up 6 rungs before the heat of the flames caused him to come down 10 rungs. After some minutes he was able to climb 18 rungs to the very top of the ladder.
Question:
How many rungs did the ladder have?
Bartender
Situation:
There are two twin old men that go into the same bar every day. The bartender at the bar hates one of the twins, but there is only one way he could tell the difference between them: The one that he hates drinks very slowly and the one that he likes drinks fast.
One day the bartender decides to kill the one that he hates. So when they came in that day he put the same amount of the drink in their cups, the same amount of ice, and the same amount of poison. When they are both done with their drinks the one that the bartender hates dies, but the one he likes lives.
Question:
How is this?
Hats
Situation:
There are 4 people sitting in a row, trying to win a riddle.
The one in front was wearing a red hat.
The second from the front was wearing a blue hat.
The third from the front was wearing a red hat.
The last was wearing a blue hat and is blind-folded.
Each of them was informed that they are all wearing a hat, the last person is blind-folded and that there are 2 red and 2 blue hats. They can only see the persons in front of them and are not allowed to turn around and see behind them.
Question:
The one who guesses the color of his hat wins the prize. Who is it?

Firefighter
Situation:
A firefighter stood on the middle rung of a ladder, spraying water on a burning house. He then climbed up 6 rungs before the heat of the flames caused him to come down 10 rungs. After some minutes he was able to climb 18 rungs to the very top of the ladder.
Question:
How m ... Open whole case