When I last took the exam, the case studies were placed at the end of the exam. You have to read them very carefully because some of them are worded in such a way that it is easy to miss key information. Some of the case studies give more information than others, so the length varies. Just remember that unless instructed otherwise, you are to make your decision based on the information provided, and do not make assumptions.
Personally, I did not purchase any question bank at all.