Cut the Knot: Probability Riddles

He who untied the Gordian knot would rule all of Asia

So goes the legend of the tricky knot of Gordius, king of Phrygia.Many had tried; many had failed, but Alexander the Great simplycut the knot with his sword. He went on to conquer most of Asia,eventually reaching as far east as Northern India.
Cut the Knot is a book of probability riddles curated to challenge the mind andexpand mathematical and logical thinking skills. First housed on cut-the-knot.org,these puzzles and their solutions represent the efforts of great minds around theworld. Follow along as Alexander Bogomolny presents these selected riddles bytopical progression. Try them for yourself before reading their solutions. Just like itwas for Alexander the Great, the non-trivial, unexpected solution might be exactlythe one you need.