If you're worried about maths in Year 10, I'd say 3U would prove to be a challenge for you in the future. However, I would STRONGLY suggest picking 3U maths, and riding with it as long as possible. Most uni courses have a restriction for students who didn't do at least 3U.
You can always drop the first thing next year, however, you cannot pick up 3U if you choose to do 2U.
As a 4U student, I'm not particularly familiar with the advanced syllabus and the level of difficulty that they assess. From feedback, this year's 2U test was quite hard (maybe they're making it harder?). But 2U is mainly focused on statistics, and very basic maths topics, like logs and sequences and series, etc. 3U is a fair jump in difficulty, going into more advanced topics in maths --> perms and combs is a killer
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