This book by the founder of the genre of scientific and entertaining literature, Russian scientist Ya. I. Perelman combines two works of the author: "Entertaining Mathematics" and "Entertaining Arithmetic". It aims to instill in its reader a taste for the study of mathematics, arouse his interest in independent creative pursuits and introduce him to the world of scientific knowledge.The book contains fascinating stories-tasks with unusual plots on mathematical topics, curious examples from everyday life, puzzles, comic questions and experiments - and all this through the game, easily and naturally.The formulation of problems, their arithmetic and logical methods of solving and the conclusions arising from solutions will arouse interest not only among young novice mathematicians, acquaintances only with elements of arithmetic, but also for readers well versed in mathematics.The author's style of writing corresponds to the 20s of the twentieth century and has been preserved unchanged.