Enough to determine competency. It's not based on number of sections or questions. The test is adaptive, asking questions of varying difficulty. Obviously, if you completely fail a "section", you won't be judged competent and will fail the test.
Know your stuff and you will be fine. And remember a lot of the questions that not all of the answers are "wrong" just the may not be the best/first course of action... Get good at narrowing down multiple choice too.