The syllabus covers roughly 95% of what a suitably motivated pilot would learn over the average career, but about 40% of it is useless at the beginning. To answer your question, it's just around O level statndard if you go that far back as I do
Basic trig, pohysics. Just a lot to remember.
You will not pass the current exams on knowledge alone. You will need the help of a database, not to learn the answers but to get used to the daft questions (which seem tio be more concerned about your grasp of English than your knowledge) and to watch out fior the ones that are actually wrong.
The good news is that everything is being given a thorough overhaul and the new Learning Objectives (I am sitting in EASA right now doing this) will be much leaner and meaner and we hope to get the NPA ready fior comment by the end of the first quarter of 2016. A lot of industry people are putting a lot of voluntary work into this, and I think people will be pleased with the results.
The question database will take longer to sort, but all development on questions for LOs that will be changed or deleted has been stopped and resources channelled into areas that are currently a bit short on questions anyway.