I have collected (and made) a lot of cool maths & logic puzzles over the years.
As too many Facebook maths problems today seem uninspired, I have decided to start posting from my collection.
This particular puzzle is from The Moscow Puzzles. This book is awesome, sold millions of copies, and is one of the best “brain teaser” books ever (first released back in the 1950’s).
It’s not a “modern self help book” so nobody is trying to market it, which means it can typically be purchased for around $4. Not bad for a book so full of great puzzles and rustic Russian charm.