Can you solve this slippery maths puzzle that doubles as a morality tale?

The International Mathematical Olympiad (IMO) is an annual competition for the brainiest of high-school maths whizzes in the world. This animation from the US YouTuber Grant Sanderson, who creates maths videos under the moniker 3Blue1Brown, breaks down a question from the 2011 IMO that proved especially challenging to competitors. Between Sanderson’s methodical analysis and the nifty animations, the maths-minded might convince themselves that they would have come up with the answer all on their own. But Sanderson, ever the savvy instructor, crafts his lesson around how to find the solution as well as being mindful of how knowledge is obtained. In doing so, he transforms an algebra puzzle into a lesson on empathy, pedagogy and the nature of discovery.