Who has never completed a crossword or arroword, or played a game of Scrabble? Word games are clearly an established part of our culture. But what about number games, you may ask? Fans of crossnumber puzzles and arithmetic games abound... among Tangente readers! Among the population as a whole, however, there is still plenty of room for growth. Thanks to Tangente, the gap is gradually closing. Yet working out with numbers is every bit as exhilarating as playing with letters. Éric Trouillot, who will of course be there on Sunday, December 3, regularly invites people to discover this pleasure through small, game-based mental arithmetic challenges, including the famous Mathador.
Dominique Souder is the best-known of France's "mathemagicians." Among his many appearances at Tangente's 30th-anniversary celebration, here is a trick to be performed by two magicians in cahoots, designated M1 and M2. M1 asks a spectator to choose a day of the month, as a number from 1 to 31; the audience and M1 are told the number, but M2, who is standing some distance away, is not. M2 is called over, and M1 adopts a pose of telepathic communication, his head resting in his hands, to transmit the chosen number to him. M2 immediately reveals it.
Here is how it works: M1's right hand plays no part, but the five fingers of his left hand represent the binary place values 1, 2, 4, 8 and 16 when extended, and 0 when folded down. M2 visually reads and adds these values as a binary number: the finger farthest to M2's right (the left thumb) corresponds to 1, while the finger farthest to his left (the left little finger) corresponds to 16. To get the trick right, M2 adds all the values represented by the extended fingers.
The Mathematical and Logical Games Championship launches its 32nd edition in 2017–2018 (see the FFJM website to take part). This unique competition is open to everyone, from elementary schoolchildren to experienced adults. Each puzzle is presented in a playful, entertaining way, and contestants need give only an answer (together with the number of solutions if there is more than one). Puzzles for every age group and ability level will soon be available in the book Jeux mathématiques astucieux et faciles, due out in January. They cover numerical, geometric and logical topics. Michel Criton, president of the Fédération française des jeux mathématiques (FFJM), will present them during the 30th-anniversary celebration.
