Martin Gardner can be considered one of the best there ever was in writing about mathematics. His essays are always entertaining and contain enough content to suggest other applications of the main point of his thesis. This book contains a series of short puzzles, most of which have quick solutions based on an "alternate" form of reasoning. That form is described as an "Aha" moment, where looking at the problem a different way leads to a simple solution to what appears to be a hard problem.
Illustrated with cartoons and full of humor, it is readily enjoyable by many people who wouldn't normally touch a book on recreational mathematics.
---BOOK (PDF packed in *.7z - In order to open .7z files you'll need 7-zip)