By Royal V. Heath. 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, interest rates worked in one’s head, such entertainments as the Lost Digit, and Psychic Bridge.  Over 30 pages of magic squares, triangles, cubes, much more.  Inexhaustible source of stimulating mathematical recreation. 76 illustrations, 128 pages, 5 3/8″ x 8 1/2″.