How low can you go

And still pass a maths exam? By which I mean get a c.
At a level, the pass mark is about 60%.
At university the pass mark is a pretty uniform 40%.
In the Scottish highers this year it is 33% and I heard a few years ago it was 29% on an AQA GCSE paper. Beating them all though is the 15% a trainee teacher got on an intermediate GCSE maths paper. She continued on the course, so I suppose she mist have passed the exam.