Here is my personal opinion.
The HFSJ book questions with multiple possible answers, doesnt tell you how much choices are correct. Whereas on actual
test, it does mention it. It probably adds extra 10%.
For rest 10%, it is coming from the level of questions, and how you perform on the actual test. The tests have a way of measuring your skills as you solve them.
Interesting thing to try on the test would be, to get all the questions answered wrong, and mark all those questions, so that you only get easy questions. Once you have all the 69 questions, mark the correct answers.
Aruneesh