To the attention of the young, and not very, the reader is offered a book series composed of once widely known works of the talented domestic popularizer of science Yakov Isidorovich Perelman .. The beginning of the series, which you now hold in your hands, written by the author in the 20s of the last century. Immediately became extremely popular, it has since been virtually unpublished and is now very rare....... The book is devoted to mathematics. [ Here are collected a variety of mathematical puzzles, many of which are clothed in the form of small stories .......... This book, as I said. and . Perelman, "is not intended for those who know everything well-known, but for those to whom it is yet to become known." All books in the series are written in the form of a casual conversation , Includes original calculations, successful comparisons in order to encourage scientific creativity , illustrated with a variety of puzzles, Complicated Questions , Interesting stories , Funny things to do , Paradoxes and Unexpected Parallels . The author's style of writing is preserved unchanged, the statistics given in the book correspond to the 20th years of the twentieth century.