How to Answer Brain Teaser Interview Questions
I have been asked in some ib interviews, and have another coming up where I KNOW they'll ask me this question & I'm just wondering how to go about answering questions similar to this in an interview:
"How many taxis are there in NY"
"How many baseballs can you fit inside this room"
"How many stop lights are there in NY"
Does anyone have success or a strategy answering these types of questions or know what the interviewer is looking for? I know they want to see your thought process and how you go about it but just wondering whats a good way to answer this type of question
Mastering Brain Teaser Interview Questions
Consulting, banking, and hedge fund interviewers often times like to ask brain teasers to assess a candidate’s critical thinking skills. When answering these questions, it is important to think out loud while you work towards an answer so that the interviewer can see your thought process as that is really what is being tested. We walk through a sample question below.
"How Many Light Poles Are There in Manhattan?"
- Let's assume there are 120 blocks in Manhattan
- Let's then assume that on each large block there are 30 light poles
- 120 * 30 = 3600 light poles
From that exercise, you can see that it is important to state your assumptions out loud rather than saying "3600 light poles" without explaining how you got there.
Another important point to make is that simplification is key since you will be doing math in your head. While there are many more blocks in Manhattan than 120, that is a large enough number to seem somewhat realistic and an easy number to multiple with in your head. Don't make the math harder for yourself - stick with multiples of 10 in all scenarios.
You can check out a detailed walk through of how to answer these brain teasers below.
Answering Brainteasers With Only One Right Answer
This method works for brain teasers that do not have a specific answer - however, there are some brain teasers that have only one answer and you are meant to find it. These kinds of questions look like this:
Source: https://www.braingle.com/brainteasers/teaser.php?op=2&id=363&comm=0
When answering questions with a defined answer, make sure to think out lout and if you get too stuck, don’t be afraid to ask for a push in the right direction.
Check out a list of Investment Banking Brainteasers from Business Insider.
Read More About Brain Teasers on WSO
Preparing for Investment Banking Interviews?
The WSO investment banking interview course is designed by countless professionals with real world experience, tailored to people aspiring to break into the industry. This guide will help you learn how to answer these questions and many, many more.
Pick up a copy of Case in Point - great pointers there for this type of "market sizing" brainteasers. Even if you aren't going into consulting, I find it a great book to have just for interviews.
I had a very similar question in my interview and not sure I answered this specific question correctly (or according to the brainteaser books) but did get the offer. I was asked, since I was from TX, how many Dallas Cowboy jerseys were sold in the US last year? I basically made a list of assumptions and with each assumption attempted to narrow down my answer. The interviewer questioned/belittled/agreed with every assumption I made. Assumptions went something like... Total TX Population---Total Football Fans --- Total Pro Football Fans---% who purchase a Jerseys---Texans Vs. Cowboys Split--- used this to make an assumption on Cowgirl fans out of state and came up with a #. Again this may be an awful answer but know i got through it and got the offer so assuming it wasn't completely awful. Good luck and practice your quick math skills and don't be afraid to use easy round numbers.
Exactly. The answer doesn't matter. It's how you got there.
If you would have answered, "I would Google how many Dallas cowboys jerseys were sold last year and then get the exact number from a sales website" you would be less likely to get an offer than by going through all those assumptions and be completely wrong.
Like for the how many stop lights in NY... Just for Manhattan as a reference, you could say that Manhattan is x miles wide by y miles long. There is a street every .1 miles (or whatever it is), and then an avenue every .3333 miles which would give you XY.1.3 (do calculation) possible intersections. Then assume that due to parks and blocks that don't follow the normal estimated .1x.33 square, that only 90% of those intersections exist. Then assume that 95% of those intersections have lights and that would be your answer.
You could times that number by 4.5 to get the total for all of NYC. The boroughs are bigger, but not as dense with their traffic lights so there's probably the same amount as Manhattan, except Staten Island and the Bronx because they aren't as large as Queens and Brooklyn so that's why you'd scale down to 4.5.
If you said all that in an interview, I'm sure that any interviewer would be satisfied with that answer.
Like what skinnayyy said, I think they just want to see you think through the problem without getting all flustered/confused.
Cap and trade.
Brainteasers - General approach? (Originally Posted: 10/07/2007)
How did you guys prepare for brainteasers, case study, and mental math parts of the interview? I read the vault guide, which provides a very general approach to it. Any helpful tips for doing math quickly?
you just have to practice the math. you should know how to find percentages and fractions really quickly in your head. during my interview last week, the guys was like, "you dont seem very analytical to me." as i began to respond, he point blank asked me what was 7/16. i think getting it right helped me out alot.
That's more of an S&T type question, you got that for IBD?
actually, yea. the guy was a dick though. i'm not sure whether its just me, but i feel like i've been getting absurdly difficult first-round interviews. ive had people straight up grill the shit out of me
value this perpetuity stream:
years 1, 2, 3, 4 from now on forever you get 10, 20, 30, 40 dollars and so on in the obvious way.
discount rate is 10%.
what's the total value of that cash flow?
Present Value of a Growing Perpetuity, is that not the same as the Gordon Growth Model?
D1/(K-G) or Payment/(K-G), for this equation. Don't you need G to figure this out?
mj - that is a terrific question. I had some fun with that one.
Are you supposed to do that problem in your head, mj?
anyone know the answer
yea my initial thought was that you needed G. perhaps this what you'd say during the interview?
yea my initial thought was that you needed G. perhaps this is what you'd say during the interview?
Another way to look at it is a series of perpetuities with payments of 10, with each subsequent perpetuity being shifted out one year.
So what you have is the following:
10/0.1 + 10/0.1/(1.10)^1 + 10/0.1/(1.10)^2 + ... +10/0.1/(1/10)^n
Each of the 10/0.1 simplifies to 100, so what you have is the following:
100 + 100/(1.10)^1 + 100/(1.10)^2 + ... + 100/(1.10)^n
This is basically just a perpetuity of 100 discounted at 10%, so you can just do 100/0.1 for 1000, and add back the first term (since doing 100/0.1 will catch all the terms starting with 100/(1.10)^1 onwards).
You end up with 1100 either way.
http://www.braingle.com/Logic.html
If you would like, I can give you the numbers of the standard ones asked.
A little history of the beginnings of these interview questions--
They originated as Oxbridge interview questions, adopted by the Euro banks in London, then the US banks in London. Now it seems in the last couple of years, they have become a more popular in US and Asia-Pacific consulting and IB interviews. It is about the thought process, as well as the answer.
Mental math questions are fairly simple math taught in most European schools for decades. No pen and paper allowed.
While students in the US and Asia are drilled for standardized testing, European counterparts learn brainteasers and mental math tricks.
http://users.telenet.be/jo.roel/Riddles/index.html
Under math-riddles 2, 3, 5, and 7 are often used.
Under physics -1 and 2
generally use these in a group exercise. European interviews use brain teasers more in individual interviews.
those were fun thanks
I must say Jimbo, I find you to be the most delightful and insightful trader (and poster on such boards) that I have ever come across.
how many tennis balls can u fit in a 747 ? How many planes are flying over the US right now ?
"I must say Jimbo, I find you to be the most delightful and insightful trader (and poster on such boards) that I have ever come across."
too kind, too kind....
sol, which numbers are commonly asked from the first link you posted?
Logic= # 13, 25, 58, 240, 262 Logic Asia Group Exercise= #70, 128, 280 Probability= #11, 15, 34, 43
There is one interviewer in the NYC office who always asks the Birthday Probability one....and loves to argue the thought process! What a bozo.
The lily pad question and the 3.15 time on the clock angle have been this years favourites. They are on the next link of riddles.
Just make sure you don't blurt out the answer....give it that slow, thinking out loud stream.
I haven't gotten one single brainteaser the whole time through multiple BB interview processes. Got one at Jefferies, but that's it. I don't know, maybe I've gotten lucky, but I've presonally gotten more accounting/fit questions by FAR.
Maybe they pull them out if you seem uneasy, I dunno.
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