Can You Solve This Clever Counterfeit Coin Conundrum?


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockJun 4 2021, 17:44 UTC
gold coins on a scale. Image Credit: focal point/

gold coins on a scale. Image Credit: focal point/

When it comes to probability puzzles, a classic of the genre is a single counterfeit coin within a bunch of real ones. Educator Jennifer Lu for TED-Ed has crafted a particularly brainy one. You are the greatest mathematician in an Empire and you’ve been imprisoned for criticizing the despotic ruler’s tax laws.


Your chance at freedom comes when one of the 12 governors is accused of paying taxes with a counterfeit coin. Your job is to find which one is the fake one, which might be lighter or heavier than the others.

Unfortunately, the Emperor is not a patient person and quite a cheap one. So you only got a scale, a marker, and three attempts at weighing the coins to work out which one is the fake one. Can you do it?

We don’t want to give you any spoilers but just a little hint. The marker is more important than you might think at first!

Good luck!