The Assassin Puzzle | Infinite Series

17th May 2018

Imagine you have a square-shaped room, and inside there is an assassin and a target. And suppose that any shot that the assassin takes can ricochet off the walls of the room, just like a ball on a billiard table. Is it possible to position a finite number of security guards inside the square so that they block every possible shot from the assassin to the target?

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Solution to the Assassin Puzzle:

Previous Episode:
Instant Insanity Puzzle

Let’s walk through this puzzle a little more precisely. First, instead of thinking of a physical room with actual people inside, I really want you to think of a square in the xy plane. Pick any two points in the square, and let’s call one of those points A for “assassin,” and the other point T for “target.” Now a “shot” from the assassin is really just a ray emanating out of the point A which can, like a ball on a billiard table, bounce back and forth between the sides of the square. But unlike an actual game of pool, let’s assume the trajectory has constant speed and that it can bounce back and forth for forever!

Written and Hosted by Tai-Danae Bradley
Produced by Eric Brown
Graphics by Matt Rankin
Assistant Editing and Sound Design by Mike Petrow and Linda Huang
Made by Kornhaber Brown (

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