Mathdoku Puzzles can be solved by combining the four main mathematical functions of addition, subtraction, multiplication and division. To train the brain the puzzles are offered without any instruction. There are important keys to be found but no fixed starting place and no method of progression that can be learned as a strategy. The brain is forced to dart between competing theories. It's impossible to solve puzzles without the scientific process of trial and error and that's the rationale behind these puzzles.

KenKen™ was invented by a Japanese mathematics teacher Tetsuya Miyamoto and introduced to The Times via Robert Fuhrer of Nextoy and Chess Champion Dr. David Levy and recognized for its depth and magnitude by The Times features editor, Mr. Michael Harvey. KenKen™ brain training puzzles are a trademark of Nextoy, LLC. Toy inventor Robert Fuhrer, founder of Nextoy, discovered KenKen™ (aka KEN-KEN) in Japan as the original books published by educational publisher Gakken Co., Ltd. as Kashikoku naru Puzzle, and has been instrumental in introducing them to the western world.