They say it's much more difficult than the real exam. But that's not necessarily bad, on the contrary. The more questions you fail, the more chances to learn new things you will have. You need to not just do the quizzes and see how many questions you got wrong, you need to do the quizzes, and then review each question in depth, take notes, do sample programs to illustrate the points, etc. Needless to say, this takes a lot of time.
All code in my posts, unless a source is explicitly mentioned, is my own.