I believe it is approx 80% if my memory serves me correctly. It is dependant upon which questions you are asked also as some gather more points than others.

Waheed is more clued up on this.....

No question is a stupid question!

The passing score is 75% (18 Questions) and you can miss 6 questions.  This was when I took the test (Feb 2006).

You can also call your test centre and they will confirm it.