The collection "Tasks for children from 5 to 15 years old" caused a lot of reviews. Both children and adult readers often regretted that there were only mathematical problems - after all, all natural science deserves an equally active, creative attitude towards itself. Now I answer these wishes - following Jan Amos Kamensky rather than modern teachers, that is, always striving to be understandable to a reader who does not have prior knowledge (but as inquisitive as most adolescents).