When you’re applying for an engineering job at one of the most competitive tech companies in the world, it’s not enough to simply be good at math—you need to know how to apply the principles you’ve learned practically, and often creatively. That may be why some of those same companies are rumored to include seemingly random, surprise math problems and brain teasers as part of the interview process.
Amazon, for instance, supposedly asks its software engineers to solve math problems like this viral ‘hanging cable’ challenge. In a recently unearthed viral video, YouTuber and mathematician Presh Talwalkar, author of The Joy of Game Theory: An Introduction to Strategic Thinking, highlights another problem rumored by many people to have surfaced during Google’s famously competitive interview process. The question reads:
There are 25 horses. What is the minimum number of races needed so you can identify the fastest 3 horses? You can race up to 5 horses at a time, but you do not have a watch.
On his blog, MindYourDecisions, Talwalkar expands on the question to help put the challenge more precisely:
There are 25 mechanical horses and a single racetrack. Each horse completes the track in a pre-programmed time, and the horses all have different finishing times, unknown to you. You can race 5 horses at a time. After a race is over, you get a printout with the order the horses finished, but not the finishing times of the horses. What is the minimum number of races you need to identify the fastest 3 horses?
Talwalkwar—who is clearly Google material himself—uses a deceptively simple three-step process to find the answer. You can read it here along with an exhaustive analysis of why the procedure works, or simply watch the video below for Talwalkar’s full breakdown on his MindYourDecisions YouTube channel.