A box contains 7 fiction books, 5 non-fiction books, and 3 biographies. Two books are selected from the box at random without replacement.
Draw a tree diagram to represent this information.
Find the probability that the two books selected are both biographies.
Given that at least one of the books selected is non-fiction, find the probability that both books are non-fiction.
200 exam-style questions on OCR A Level Maths 2.3 Probability, covering 2.3.1 Mutually exclusive and independent events, 2.3.2 Diagrams to assist probability calculations, 2.3.3 Conditional probability (A-level only), 2.3.4 Conditional probability from first principles (A-level only), and 2.3.5 Modelling with probability. Each one has a worked solution and a mark scheme showing where the marks go.