ducd, that's the point. By only giving you half the answers, they provide enough material to learn from and test yourself against. Instructor's manual has all of the answers, so its up to the teacher to provide them.
This is fine for university students, but for anyone else, it is deeply frustrating. I don't want to have to email the author of a book merely to obtain solutions to the exercises; after all, the author may have died since they wrote the book.
