Really depends on a few factors for your internal mark:
- how your cohort performs in externals
- what's your internal rank/position and the relative gap between you and your peers
You could get 40-70s in your school assessments (because your school sets insanely difficult exams) and still be coming 1st. Then in externals, you scored the highest exam mark of let's say 95.
You'll get 95 as your internal mark (you're ranked 1st internally and will receive the highest external mark as your internal) and keep your 95 external mark. Average it out and your final HSC mark will be 95 (note that your exam mark is an aligned rather than raw mark) despite getting 40-70s in school.