## The Running Dog

"Yes, when I take my dog for a walk," said a mathematical friend, "he frequently supplies me with some interesting puzzle to solve. One day, for example, he waited, as I left the door, to see which way I should go, and when I started he raced along to the end of the road, immediately returning to me; again racing to the end of the road and again returning. He did this four times in all, at a uniform speed, and then ran at my side the remaining distance, which according to my paces measured 27 yards. I afterwards measured the distance from my door to the end of the road and found it to be 625 feet. Now, if I walk 4 miles per hour, what is the speed of my dog when racing to and fro?"

View the solution

Holey Sphere!

# Understanding Coronavirus Spread

A Question and Answer session with Professor Puzzler about the math behind infection spread.

# Blogs on This Site

Reviews and book lists - books we love!

The site administrator fields questions from visitors.

Like us on Facebook to get updates about new resources