Mathemagic: Magic, Puzzles and Games with Numbers (Dover Recreational Math)

More than 60 new puzzles and stunts based on the properties of numbers. Easy techniques for multiplying large numbers mentally, identifying unknown numbers, determining the date of any day in any year, such entertainments as The Lost Digit, and Psychic Bridge. Over 30 pages of magic squares, triangles, cubes, more. 76 illustrations.