If this helps, my sibling got a HSC mark of 40/50 (just band E3 = band 5 [80%]) for Extension 1 Maths and gained a UAI of approximately 88 (if that helps). But mind you - they also did religion and got 44/50, maths and got 86/100, physics was in the 50's, standard english in the 70's, PDHPE low...