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 studying mathematics, to arouse his interest in independent creative pursuits and introduces him to the world of scientific knowledge. The book contains fascinating story-challenges with unusual plots on mathematical topics, interesting 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 solution and the conclusions arising from the solutions will arouse interest not only among young novice mathematicians familiar only with the elements of arithmetic, but also among readers well versed in mathematics. The author's style of writing corresponds to the 20s of the twentieth century and has been preserved unchanged.