Brainteasers still relevant?
Are brainteasers still common in IB interviews today? And how much do they matter in terms of getting an offer?
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was asked a very simple one at a superday in oct of 2017. got it right and spoke with the person who asked it after. they said they just asks that single brain teaser as a metric to see if they know extremely easy statistics.
The q was: if you have two different kinds of socks in a drawer and you need to grab a pair of socks out - with the lights completely off, what is the minimum amount of socks you can grab out of the drawer to guarantee that you have a pair?
I was asked one in a set of interviews this spring that was mental math. I think it was like "What is 27^2?"
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The answer is 3 (assuming you can put a sock on either foot). It's the pigeonhole principle.
No problem. Say you have an infinite number of socks, but only two types in this drawer- Sock type A and Sock type B. If you randomly select two pairs of socks, you might end up with 2 Type As (A | A) or 2 Type Bs (B | B) OR you could wind up with 1 Type A and 1 Type B (A | B). Without turning on the lights to see, you have no way of knowing what combination of socks you pulled out. However, when you pull the third sock out it doesn't matter, because you're guaranteed to have a pair of socks.
The following combinations are available for three pairs of randomly selected socks:
(A | A | A) or (A | A | B) or (A | B | A) or (A | B | B) or (B | B | A) or (B | B | B) or (B | A | B) or (B | A | A)
Therefore, you are guaranteed to have a matching sock after three sock pulls!
If someone asked me a permutation/combination question now, I’d be ready to grab them from the other side of the table. Once you’re out of school, those questions are just pointless.
But I did get one not too long ago that was like “how many golf balls are sold in America each year”. That one was actually pretty fun.
I think brain teasers are becoming less and less common. I had 3 superdays (two with MM firms, one with an EB) and was not asked a single brainteaser/mental math question. I do think that some EBs (Centerview pops into my head) are more likely to test your raw brain power with brain teasers.
Overall, though, I think it is more interviewer specific. If you have a 3.8+ GPA from a target/semi-target with tough majors, they know you are smart, and are probably less likely to ask you brain teasers.
If you nail the technicals and are able to come across as likable, I don't think they will care if you bomb brainteasers/mental math as long as you give them a decent shot.
I always ask 1 of 2 brain teasers I have on hand. Not because I care about you eating the right answer, but it’s a good way to see how people think. If you do really well on all the technicals but not the brain teaser, things aren’t going to change much and it won’t be a ding. But if you did ok on the technicals and crush the brain teaser (and clearly not because you just knew the answer already), that might be enough to get you over the edge.
I have two go to questions: 1. How many hours a day do you have to work, in order to work 100 hours a week? 2. If you get to the office at 9:00 am, and you work 14 hours, what time do you leave the office
I've had a few people opt out, realising that they don't want to do this, which is great, because it's saved us both some time. Also, I've seen people that really don't think, some of my favourite responses are: - "You need to work 20 hours a day" okay, I guess if you really want the weekend off - Girl who thought that 15 hours was 9:00 am - 9:00 pm - Guy who legitimately spent three agonising minutes dividing 100 by 7 (I said we could move on but he insisted that he could do the math in his head) - Kid who said - yeah, but no one actually works until midnight every day, that's just a story they tell you to scare interns
We don't have much turnover here but I did get to interview someone recently and made a point to get at least one of these types of questions in. Sometimes these types of questions would rattle my cage when I was active in my job search, so I think its good to get at least one in to see how the person thinks and reacts under pressure.
I got this question from Bridgewater but I used it in the interview and have adopted it as my default brain teaser for future interviews. Just about everyone in my office got this question wrong when I asked it as well. Anyways, the question is:
You're on a raft in the middle of the ocean, you're allowed one item, what is it?
The wrong answer is just to say some random item or the first item that pops into your head. The correct answer is to start blasting off questions. In the original question you have absolutely no context to answer it, just as if I were to ask you to put a price target on some company you've never heard of. So what you want to hear is the person start asking things like how did I get there? Where am I geographically? What time of year is it? Am I alone?... Eventually asking enough questions to reasonably form a more educated answer. I think it's a good one to ask for a research type role. The kid we interviewed only asked one question, but that was better than most people in my office, we hired him.
What if my one item was a fully gassed helicopter or a cruise ship. Then answering right away seems like a good idea :)
I would've awarded points for cruise ship haha
DB Houston office asked me "How many stoplights do you think there are in the city of Houston?" and asked me to explain my thinking.
Yeah, that's a variation on 'how many piano tuners are there in Greater New York area', variations include: - How many windows are there in x building - How many ties are there in the UK - How much money does the coffee shop next door make in a day
Its just a way to see how thoughtful people are and how they problem solve.
That's a market sizing question, quite common in consulting (and sometimes in IB)
I was asked a few questions related to how certain macro events would affect their coverage sector. IMO after undergrad its much less common to get generic brain teasers like "how many light bulbs are there in new york city" etc... They may ask you some though provoking questions related to their industry / sector but in my experience I only had those generic types of brain teasers during undergrad interviews
These types of questions tend to be more along the lines of "this question can't really be answered but we just want to see if you will ask further questions to clarify the problem at hand and how you work through your assumptions" more than "answer this probability and statistics question".
Aforementioned "how many golf balls are sold in america each year" would be an example of the former. -USA has about 325 million residents -Golf is not a cheap sport, lets assume only about
Couple I've encountered are:
How far apart are the hour and minute hands on a clock at 3:15
You have 10 stacks of 10 coins. All coins weigh 1 gram, except for in one of the stacks which consists of coins that weigh 2 grams (so 90 coins weigh 1 gram and 10 coins weigh 2 grams). You have an electronic scale ( not a balance). How many times do you have to use the scale to figure out the heavier stack?
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