This small collection differs from other books of similar content in that it offers less used material, and in the way it is processed it is closer to school arithmetic, affecting its various departments. In order not to turn the pleasant play of the mind into a tedious activity, too serious for entertainment and often too fruitless for serious work, the author avoided difficult questions and selected only such material that is quite strong for most readers. Although the book is meant for readers who are familiar only with the elements of arithmetic, there will be pages in it that are not without interest, perhaps, for those who are more knowledgeable. A diligent request to such readers is not to refuse to inform the author about the shortcomings of the book they have noticed .