Martin Gardner 
Gardner’s Workout [PDF ebook] 
Training the Mind and Entertaining the Spirit

For many decades, Martin Gardner, the Grand Master of mathematical puzzles, has provided the tools and projects to furnish our all-too-sluggish minds with an athletic workout. Gardner’s problems foster an agility of the mind as they entertain. This volume presents a new collection of problems and puzzles not previously published in book form. Martin Gardner has dedicated it to "all the underpaid teachers of mathematics everywhere, who love their subject and are able to communicate that love to their students."