"Terrible problem books" by G. Oster is a collection of problems in mathematics that can be easily solved by younger schoolchildren and even preschoolers. There is nothing complicated about them. But there are funny and scary stories about restless twins, one and a half year old villain Kolenka and other active children who regularly get into trouble. Thanks to them, the problem book easily turns into a fun security manual, in which from scary to funny - one step.