Stupid interview puzzles

My high school friend Gary pointed out an interesting article — Elon Musk asks this tricky interview question that most people can’t answer — about Elon Musk and his hiring techniques at SpaceX, which got me wondering about this popular idea of challenging job applicants to solve the interviewer’s favourite puzzle.

Briefly, Musk asks people this question when hiring –

the puzzle

“You’re standing on the surface of the Earth. You walk one mile south, one mile west and one mile north. You end up exactly where you started. Where are you?”

and in the article above they even have a video where they ask people in the street this question.

one answer

One answer, and by far the most common one, is The north pole. If you’re at the north pole and you walk a mile south, and a mile west, and a mile north, then you’re back at the North Pole.

another answer


Musk then asks, Where else could it be? and apparently sits back and waits for you to come up with another possibility, namely at a point near the South Pole. If you are just a wee bit north of the south pole, then you can hike one mile west in a perfect one-mile-circumference circle around the pole and be back where you started. Any point one mile north of this circle would be another answer.

The article says –

Once the applicant arrives at this answer, Musk then asks, “Where else could it be?” A second answer to the puzzle is near the South Pole, where the Earth has a one mile circumference. You’ll walk one mile south to reach this circle, trace that mile-long circle’s path, and return one mile north to your starting point. Fewer engineers give this answer, according to Vance.

Like this helpful not-to-scale diagram I just whipped up.

If you want to get all mathie here, a path of circumference 1 mile would have a radius of 1/(2π) miles, so starting at a point of 1 + 1/(2π) miles north of the pole would be an acceptable answer to this puzzle.

Of course that’s not just one point. ANY point on the circle 1 + 1/(2π) ~= 1.16 miles north of the south pole is an answer.

the discussion

“Fewer engineers give this answer”, the article says, and it continues to say…

Luckily for his applicants, Musk doesn’t place much emphasis on whether applicants give the right answer, explains the author. Instead, he uses their response to analyze how they process information and approach problem solving.

Given SpaceX’s mission, to send humans to Mars, employees must be able to reason their way through problems and find novel solutions.

here’s what bugs me

You know what, Elon, there are even more answers to this puzzle. What if, in walking west, you went twice around the south pole, along a circle of circumference 1/2 mile, with radius 1/(4π)? So now any point 1 + 1/(4π) ~= 1.08 miles north of the south pole is ALSO a legitimate answer.

Or if you went three times around the south pole, circumference 1/3 mile, radius 1/(6π) ? Any point 1 + 1/(6π) miles north of the south pole is ANOTHER answer. And so on.

So there are even more answers than Elon Musk, in his wisdom, is looking for.

what are we measuring here?

I suspect that interviewers, including Elon Musk, think that a puzzle like this is measuring the applicant’s problem solving ability.

I think it’s actually measuring whether the applicant has heard of this puzzle and its answers before. There are widely publicized lists of trick interview questions and answers like this, where the goal is to come up with the clever answer the interviewer wants.

Here’s a book full of interview puzzles that I enjoyed –

How Would You Move Mount Fuji?: Microsoft’s Cult of the Puzzle — How the World’s Smartest Companies Select the Most Creative Thinkers

back in my day

It would not surprise you to know that I was on the Math Team in high school.

Once a month or so, every high school in the city would send a five person team to my school, London Central, and we’d do problems in the cafeteria and declare a winner.

Central did pretty well when I was on the team.

I thought I might carry this secret to my grave, but I’ll spill the beans here: one reason we did well was because the organizer of the contests was a teacher at our school, and he happened to go to the school library to consult books of puzzles to come up with the questions for the contest.

all of which I had previously read. multiple times. I loved those puzzle books. No wonder Central usually won these contests.


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