A bag contains 11 blue counters, 10 red counters and 9 green counters. Two counters are removed from the bag at random.
Given that at least one of the counters removed is red, find the probability that both counters are red.
368 exam-style questions on Edexcel A Level Maths Conditional Probability, covering 2.1 Set Notation, 2.2 Conditional Probability, 2.3 Conditional Probabilities in Venn Diagrams, 2.4 Probability Formulae, and 2.5 Tree Diagrams. Each one has a worked solution and a mark scheme showing where the marks go.