It's been a while since I have dont the PPL exams, but I think, and correct me if I'm wrong, the passmark is 75%. There are about 30 questions or so, all multiple choice, with each question having a choice of three answers.
Have you got the Trevor Thom book for Law? It's certainly worth it. They are also worth it for the other subjects too. Maybe think about the PPL Confuser for practice at the ppl subjects.