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Tech interview riddles

T

TubStain

Senior member
So I have an interview coming up at the end of the month. I've interviewed with them before, reached the final round and then got dropped. But anyways, they asked me a "riddle" once of "How many BMW's are there in the US" and I was stumped. They did say that I could ask them any question. But I just did not know how to begin.

Any idea how you would begin to get a solution to that?


Edit: The BMW part can be replaced by anything...like "gas pumps" "shoes" etc. The path taken to try and find a solution is more important than the solution. But I just dont know how to start.
 
I'd reply with more than there were yesterday, then I would proceed to ask questions about the company to show my interest.
 
ask how many BMW dealerships are in the US? How many cars does each dealership sell per month? How long do people generally keep the BMWs they drive? How often do BMWs survive crashes? How many BMWs get into major wrecks per month? Ask questions like that and you could make a fairly good estimate.
 
Originally posted by: minendo
I'd reply with more than there were yesterday, then I would proceed to ask questions about the company to show my interest.
Click to expand...

Somehow I don't think that's what they were looking for 😕
 
Perhaps you could ask him what assumptions you could make. For example, if you could assume the same number in every state, then you could ask him how many there are per state. Or if he knows what percent of people own a BMW, and you can estimate the US population, then you could get it that way.

So yeah, I would try some questions along those lines...
 
Questions like those are called Fermi questions, they gauge your ability to make reasonable assumptions. The cool thing is that a lot of the errors you make in your assumptions tend to cancel each other out.

Here's how I would go about it. Assume they are only talking about vehicles that are driveable. Estimate population at 250 million. Guess that on average there's one car for every 4 people, say 62.5 million cars. Now estimate what percentage of cars are BMWs... tricky. I would guess, nationwide, 1 in 50. So my answer is 1.25 million.
 
I think what you ask is this:

How many bmw's are there in the world total?

How many BMW's are NOT in the US.

Therfore, by deductive reasoning, you can tell him how many bmw's are in the us..

Its like this. You cant ask a person what caused their problem, because if they knew, they would fix it themselves, so you have to ask questions to figure out what didnt cause their problem so you know what did.

 
Originally posted by: minendo
I'd reply with more than there were yesterday, then I would proceed to ask questions about the company to show my interest.
Click to expand...

been a while since you've gone for an interview eh? Technical interviews are meant to test your knowledge and capabilities. Asking about the company to show your interest doesn't mean jack squat to the technical interviewer. He just wants to know what you do know...not what you want to know.
 
Originally posted by: Shiva112
been a while since you've gone for an interview eh? Technical interviews are meant to test your knowledge and capabilities. Asking about the company to show your interest doesn't mean jack squat to the technical interviewer. He just wants to know what you do know...not what you want to know.
Click to expand...

Well showing your interest does help, but giving a smart ass answer to an interview question doesn't.
 
Gas pumps would be much harder than BMW's. Simply because you can look at annual BMW sales for the last XX years in a single place. There are so many manufacturers of gas pumps or things of that sort that it would be very, very difficult to a) compile that information, and b) actually find a reliable sorce that documented that information.
 
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