You can probably guess that this interview question comes from Elon Musk (specifically, from a Musk biography by Ashlee Vance), given that he starts by saying “You are standing on the surface of the earth.”

Why is this a good interview question for your company? Two reasons.

First, because you can objectively get this answer wrong. Asking interview questions that determine competency can help distinguish which job applicants really know their stuff.

Second, it’s a good interview question because it has two answers.

The first answer is the North Pole. Because the Earth is a sphere, if you walk one mile south, then one mile west, then another mile north, you will just return to the North Pole. You could walk a million miles west or zero, and you’d still end up at the same place.

The second answer is any place approximately 1.32 (1 + [1 / pi]) miles north of the South Pole. If you walk south one mile, you will approach the South Pole. Then, when you walk one mile west, you will complete a full loop before walking north and returning to the place you started.

Here’s an explainer video if you’re still working it out:

Two answers, both based on the same premise. But one answer is less obvious than the other.

You can change the format of the question to fit your company, but the point is to learn whether your job applicant will come up with the complete answer or be satisfied with only partially completing the question.

Related: Will Your Interview Answers Get You Hired?