You can use sections to balance the questions in a quiz. For example you want to set a quiz with easy, medium and hard questions and randomly select 30 questions from a pool of 90. You will want the generated quiz to have 10 easy, 10 medium and 10 hard questions. Even with a random selection of questions you can guarantee the balance by grouping the questions under 3 sections (Easy, Medium and Hard) and then choosing to ask 10 questions selected randomly from each section.
