They may be useless to you (although I think even seeing examples of types of questions that can be asked serves a purpose), but the book was not written only for you. I think it is reasonable for books to have features that are useful for students in courses that assign a grade, as well as other features that are useful for students using it for self study.
It is also worth pointing out, that at least for math textbooks, there is never an expectation that a student should solve all the exercises. If you solve those that do have a solution, then you will hopefully still have a good experience and learn lots.
It is also worth pointing out, that at least for math textbooks, there is never an expectation that a student should solve all the exercises. If you solve those that do have a solution, then you will hopefully still have a good experience and learn lots.