The fifth book of the series "School Mathematical Circles" is devoted to problems about weighing and is intended for classes with schoolchildren in grades 6-9. It included the development of seven classes of a mathematical circle with detailed examples of varying complexity, tasks for independent solution and methodological instructions for the teacher. Additional tasks are also listed. For convenience, the final part of the book is made in the form of handouts. The book is addressed to school teachers of mathematics and leaders of mathematical circles.