I understand that if we do 4u maths we wont get tested on 2u stuff but we still have to learn 2u. So i was wondering, what happens if we screw up in both 3u and 4u? does that mean all 4 units will go down the drain? I've heard humors like that if you do 4u you automatically get 100 for 2u etc etc. But how exactly does it work?