Berra; you won't be able to cope with advanced. It sort of goes against normality to go UP after year 11 anyway.
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If you do twelve units, all of which are strong.. Definitely drop maths all together. I think pretty much every dux of my school in the past 4 years has advised dropping maths all together
But that’s because they were humanities inclined. The problem is most people think that maths is a necessity.. It isn’t compulsory, only English is, so if you don’t really like doing it, then don’t do it at all. You are not compelled to do maths.
No on to the marks.. General maths is scaled badly. The maximum mark you can *really* get is ~88 (when comparing with adv.) - but advanced is a pain in the arse, so it might be easier for you to get a high mark in gen. then adv. But you have to remember, that it might also be easy for everyone else, and that's the catch.
This whole thing isn't about how well you go... its about how well you go in comparison to everybody else.