To paraphrase Inc. colleague Justin Bariso, Elon Musk is at heart a problem solver. 

And his companies -- Tesla, SpaceX, the Boring Company -- attract like minds: Some of the smartest, most skilled people in the world want to become a part of the teams trying to solve incredibly challenging problems.

But how did Musk -- who reportedly personally interviewed each new SpaceX employee -- decide whom to hire? And later, after the company grew, each engineer?

According to Ashlee Vance's book Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future, Musk liked to ask questions that caught job candidates off guard. 

As Vance writes:

He might ask one question, or he might ask several. You can be sure, though, that he will roll out (this) 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?"

The answer is the North Pole, and evidently most candidates got that right.

Then Musk would ask a second question to burst their smug bubble: "Where else could you be?"

As Vance writes:

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. 

According to Vance, Musk was less concerned with whether the candidate got the right answer than in how they approached its solution.

Which, at face value, is fair enough: The way someone sets out to solve a problem is an important factor, both in terms of skill and cultural fit.

But then there's this.

Brain teasers are worse than a waste of time.

Some interviewers whip out a classic "how many?" brain teaser. Like "How many bowling balls could fit into the Empire State Building?" Or "How many trees are in Central Park?"

Others like "do a little math" brain teasers. Like "If you roll two dice, what is the probability the sum is nine?" Or "What is the sum of all the numbers between 1 and 100?"

Others prefer "hmm...?" brain teasers. Like the old chestnut, "Why are manhole covers round?"

Sound fun? Only for the interviewer.

As the authors of this 2018 study published in Applied Psychology write, ""Brain teaser interview questions are an example of aggressive interviewer behavior that lacks evidence for validity and is unsettling to job applicants ... narcissism and sadism explain the likelihood of using brainteasers in an interview." 

(There's a lovely combination: narcisissm and sadism.)

Some years ago, Google regularly used brain teaser questions in job interviews. So why did it stop? According to Lazlo Bock, the former VP of people operations, brain teasers were a complete waste of time. They didn't predict anything; they served only to make the interviewer (who already knew the answer) feel smart.

Instead, as Bock said:

What works well are structured behavioral interviews, where you have a consistent rubric for how you assess people, rather than having each interviewer just make stuff up. Behavioral interviewing also works -- where you're not giving someone a hypothetical, but you're starting with a question like, "Give me an example of a time when you solved an analytically difficult problem." 

... you get to see how they actually interacted in a real-world situation, and the valuable "meta" information you get about the candidate is a sense of what they consider to be difficult.

Which may be why Musk has apparently changed his approach.

But this question isn't a waste of time. 

Musk recently invited "ace engineers" to apply for work at Gigafactory Berlin, Tesla's European battery manufacturing plant currently under construction. In addition, Musk included the following request:

As Justin writes, that's a great interview "question." Musk sets the bar high by asking for multiple examples of tough challenges, and how they were solved. He wants to understand not just the outcome, but the process of how the candidate solved real-world problems. How they identified underlying issues and causes. How they selected specific areas of focus. How they overcame inevitable challenges and roadblocks. How they stayed the course in the face of setbacks and failures.

Not whether, and how, they could solve a brain teaser. 

Where any position is concerned, whether entry level or executive, the right candidate possesses the right skills, experiences, and attitudes.

None of which will be uncovered by the interviewer who asks, "Why is a tennis ball fuzzy?"

Next time, skip the brain teasers. If you want to know how a candidate thinks, ask for actual examples of difficult problems solved, challenging goals accomplished, or major barriers overcome.

Then you won't just gain insight into how a candidate thinks.

You'll also get a sense of what they can do.

Which is what really matters.