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It’s fair to say most people never quite know what to expect from Elon Musk, whether he’s promising to build tunnels underneath Los Angeles, or selling $500 flamethrowers to fans of his Boring Company. (Sorry, we meant Not-a-Flamethrowers.) In the past week alone, the Tesla and SpaceX CEO dropped a surprise EDM track titled “Don’t Doubt ur Vibe.”
So it may come as no surprise that interviewing for a job with the Tesla and SpaceX CEO may involve, well, a few surprises. According to the 2017 Musk-authorized biography Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future, there’s at least one question that Musk supposedly puts to prospective employees to catch them off-guard. As author Ashlee Vance puts it:
“He might ask one question, or he might ask several. You can be sure, though, that he will roll out the riddle: 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?”
When SpaceX was first hiring, Vance writes, Musk would personally interview each employee—and later, each engineer as the company grew larger. To their credit, most of them would generally guess the correct answer: the North Pole. That’s when Musk would hit them with another surprise follow-up question: “Where else could you be?”
The twist is that the riddle actually has two correct answers. “The other answer is somewhere close to the South Pole where, if you walk one mile south, the circumference of the Earth becomes one mile. Fewer engineers get this answer, and Musk will happily walk them through that riddle and others and cite any relevant equations during his explanations,” Vance writes. He adds, “[Musk] tends to care less about whether or not the person gets the answer than about how they describe the problem and their approach to solving it.”
For a more in-depth explanation of Elon Musk’s (supposedly) favorite riddle, check out this detailed breakdown from mathematician Presh Talwalkar, the man behind the popular math and science blog MindYourDecisions.