Thats where my school has a big luxury. 2 Unit classes are supposed to occur 6 times a fortnight, and ext 1 should be 3 times a fortnigt. Since ext 1 occurs on the same time as other 2 unit subjects, we get 3 extra periods a week, allowing for us to go REALLY REALLY slow in both topic and therefore solving basically every type of question possible. We got so much time that 4 unit classes are also able to fit into the timetable and have 3 classes of 4 unit a fortnight, plus after school time if needed.