The abduction of the "black square", or the new lessons of Grandfather Gavrila

Fedya graduated from the sixth grade and again rides to Grandfather Gavrila in Kvashino. This time not one, but with school comrades. Grandpa opens in the village a summer mathematical camp for the most curious! The guys are waiting for new tricky questions, difficult tasks, mathematical paradoxes and tricks. And also unexpected adventures! Schoolchildren will have to fight in a mathematical duel with a mysterious kidnapper of the "Black Square" - a beloved grandfather’s picture.
The collection includes 200 tasks for extracurricular study. It is published for the first time and illustrated by the graphics of Tatyana Leontyeva. The book is a continuation of the task of the “Lessons of Grandfather Gavrila, or Developing Vacations”. Addressed to students of the middle and high school