The book contains a variety of entertaining tasks and promotes the development of logic, analytical and mathematical abilities, memory, attention and concentration in children from 10 years old. All tasks are grouped by topic: magic squares, tasks with matches, logical, mathematical and geometric problems, crosswords, puzzles and other interesting questions. Examples of solutions, brief theoretical references, explanations of new words and concepts are provided. Answers to all tasks are given at the end of the book. The book will help children spend their free time meaningfully, learn the school curriculum more successfully and participate in mathematical Olympiads and competitions, teachers - conduct entertaining lessons and additional activities, parents - have fun organizing joint leisure time.