I bought this book because I really needed practice solving problems in QM. It lacks the mathematical background (ie, linear operators, commutators, commutating operators, and other necessary mathematics). Oh, there's a couple of problems, but as far as I am concerned, I threw the money away. It has not helped me. I am a grad student, and I never studied operators, or commutators, and of course, no one else ever uses them except in QM. I still don't know how to use operators !! My bad, like the title says, don't waste your money. The 1 star in the rating is only because they wouldn't let me submit this review without a 1 to 5 rating, as far as I am concerned it rates Zero stars