Riddle of the Week

Riddle of the Week: A Sooty Train Ride

Difficulty level: Moderate

Michael Stillwell
 
By Jay Bennett

Welcome back! We took a small hiatus from Popular Mechanics' weekly-ish series of riddles, but we are going to get back on the riddle train this week with a train riddle. Actually this week's riddle is more about dirty faces. The problem appears in the book Puzzle-Math by George Gamow, and it is credited to revolutionary Soviet astrophysicist Victor Ambartsumian.

PROBLEM

Three passengers are sitting in a train car with the window open as they travel cross-country. Suddenly, a freight locomotive laden with coal speeds by, knocking a cloud of soot straight into the passenger car's window. All three passengers' faces are covered in soot, but it happens so rapidly that none realize their own face is covered. When Miss Atkinson looks up from her book, she begins to laugh at how absurd the other two passengers look, who are also laughing.

Each passenger assumes that their own face is clean, and that the other two are laughing at each other. Then Miss Atkinson suddenly stops laughing and takes a handkerchief out of her purse to wipe her face clean.

How did she know she also had soot on her face?

HINT

In this puzzle, we can assume that all of the passengers are making logical assumptions, but Miss Atkinson is a bit quicker than her carriage companions.

Check back Friday for the Solution.