Math Dino. Entertaining tasks for 4th grade students

This notebook is a prize for those who solved the PLUS Olympiad or Dino Olympiad, and for everyone who likes to think and solve tricky math problems. In this notebook there are problems similar to those in our Olympiads. There... are also new tasks that you have not yet encountered. Perhaps even adults will not be able to cope with all these problems and find all possible solutions.
There may be not one, but several solutions: such tasks are marked with an icon.
To solve problems about carpets and pentominoes, we recommend cutting out suitable figures from paper.
We hope you enjoy these challenges.