Attention of the young and not so young reader is offered a book series, compiled from the once widely known works of the talented domestic popularizer of science Yakov Isidorovich Perelman.The book that you are now holding in your hands, which begins the series, was written 20s of the last century. Immediately became extremely popular, since then it has hardly been published and is now very rare. The book is devoted to questions of mathematics. It contains a variety of mathematical puzzles, many of which are in the form of short stories. This book, as Ya. I. Perelman said, “is not intended for those who know everything that is generally known, but for those who should still become aware of it.”All books in the series are written in the form of a casual conversation, which includes original calculations, successful comparisons with the aim of inducing scientific creativity, illustrated by a colorful series of puzzles, intricate questions, entertaining stories, funny tasks, paradoxes and unexpected parallels.The author's writing style is preserved unchanged| the statistics given in the book correspond to the 20s of the twentieth century.