How much, as a guide, do you need to get on a paper to pass ST3 (I know it probably varies quite a bit).
The marks aren't published, but the Profession indicates that for a bog-standard paper (not too difficult, not to easy) it would be somewhere in the region of 50%.
Don't get hung up about pass marks! All you can do is go into the exam in a positive frame of mind and do your best. You can't stop simply because you think you've got 60% so that's enough. If you get on the borderline they tell us they look across the whole paper to gave an all round impression. Doing say 3 long qns and nothing else may not look favourable. Just stick your head down and go for it!