Do past papers. If you don't know the answer to a question go to the textbook and find it. As you don't really need stats for prelim all you have to do is ensure you're all over the content and you'll do fine.
As someone who went to fort St and knows several people who came in in yrs 8-10 I can confirm that it is a competitive process. You will have to hand write an essay on a topic of the school's choosing in addition to providing your reports. I believe an interview is also involved. Remeber that...
I'm thinking of writing a bunch of mock trial exams for English Advanced, Economics and History and selling them for like $10 each or something (haven't worked out the specifics yet). Just wanting to see how much interest there'd be in something like this.
Im happy to take it on a case-by-case basis but as a general rule I'd say you are low income if at least one of your parents is in receipt of family tax benefit parts A and B (that's the definition usyd uses)