Grace,
The actual "passing grade" for the PMP (or any other professional certification exam) is a closely guarded secret by the certifying organization. Today, with test banks of thousands of questions of which you will get some 200 of those, the "passing grade" is variable. However, it is not arbitrary. Each question has been vetted and the difficulty of each exam is pretty constant, regardless which subset of the test bank you get.
Do not concern yourself what the "passing score" is. It does not matter. The only thing that matters in the long run is "pass" or "fail." You're not shooting for a score - your're shooting for "pass."
Harry