Jo Ann:

The registry exam is different for each person.   Since the exam is computer
administered, it can easily determine each person's ability.  The first
question given will be of moderate difficulty.  If you get it right, the next
question will be more difficult, but if you get it wrong the next question
will be easier.  Thus each question is determined by your response on the
previous question.  There is a preset pass/fail point, and you must end up
above this point to pass the exam.  That is a very simplistic answer to your
question, but hopefully will explain why each person gets a different exam,
unless two people respond to all questions in exactly the same manner.

Freida Carson