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Elon Musk used three riddles to hire the right candidate at PayPal — even smart people fail to answer

Getting hired in PayPal back in 1998 was not easy as Musk and his peers, Peter Thiel and David Sacks, had a meticulous test for candidates.

BY TIYASA BISWAS

PUBLISHED MAR 6, 2025

Elon Musk in the Rotunda of the U.S. Capitol on January 20, 2025, in Washington, DC. (Image Source: Getty Images | Photo By Chip Somodevilla)

Hiring processes are tricky, and it only gets more challenging when interviewing for a major company, say the Big 5. But Tesla CEO Elon Musk and his peers Peter Thiel and David Sacks, who together founded the financial technology giant, Paypal in 1998, ensured that potential employees had a tough time in their interviews. A candidate was bound to face three brainteasers when hoping to land a job with PayPal two decades ago. While the fintech company has since moved on to different hands after it was sold to eBay for $1.5 billion, the mathematical puzzles, said to be a staple in PayPal interviews, still hold significance today, as per The Guardian.

Silhouette of upset Australian woman over PayPal logo. (Representative Image Source: Getty Images | chameleonseye)

The brainteasers were first mentioned in Jimmy Soni’s book, The Founders, which ranged from numerical analysis to strange scenarios:

1. Find the odd one out

The first trick question included number divisors. Whole numbers have a number of unique divisors that are both odd and even. Which whole numbers have an odd number of divisors? Hint: A divisor of Z is a number that divides into Z. The number 24 has eight unique divisors– 1,2,3,4,6,8,12,24.

2. The last coin gets the prize

A circular with an unknown diameter is required to be filled with coins on its surface. You and your opponent take chances to place unlimited identically-sized coins. The coins cannot be moved after placing or even put on top of each other in any manner. The person who cannot place a coin first loses. What is your strategy to ensure that you win?

3. Measure time with burning ropes

Two ropes with varying densities along their length burn at different rates at different positions. The time taken for both ropes to burn completely is one hour. How would you use the two ropes to measure 45 minutes?

Interviewer shaking hands with candidate sitting at desk in office. (Representative Image Source: Getty Images | Westend61)

If you are looking for answers, they require quite some critical thinking. For the first brainteaser, the numbers are: 1,4, 9, 16, 25. It is explained by the formula: D x D* = Z. (Z is the whole number, D is the divisor of Z, and D* is another divisor to be multiplied with D to obtain the whole number.) For the riddle with the coins, it is advisable to first place your coin at the center of the table. In the second attempt, simply place the coin in a position exactly opposite (about 180 degrees) around the table center. This is because, in the end, there will always be space left at the edge while your opponent runs out of space, per LADbible.

Confused mid-adult businessman. (Representative Image Source: Getty Images | Image Source)

For the final trick, burn the ropes as if you were adding and subtracting time from them. Light both ends of one rope and only one end of the second starting at the same time. As the first rope burns fully in half an hour, the second will need another 30 minutes to burn. To measure the 45 minutes, light the other end of the second rope, allowing the two lit ends to meet at exactly 15 minutes. Then you have your 45 minutes when measuring from the start. The tech bros held power as the heads of PayPal, the pioneer organization that made payments easier than usual by leveraging the internet. The new owners may have found an alternative relevant to the modern age.