Terry H. Stickels, "Mindstretching Puzzles"
English | 1994 | ISBN: 0806906944 | 96 pages | Djvu | 1 MB
Contains 90 puzzles selected to increase your problem-solving powers. They include cryptarithms, asphmetics, simultaneous equations and layered thinking - more advanced puzzles than average, challenging you to replace letters with digits, break codes and much more. Answers are included.