A jar contains 12 marbles. 6 of the marbles are yellow, 4 of the marbles are green, and 2 of the marbles are purple. Sarah takes two marbles at random from the jar.
Work out the probability that both of the marbles Sarah takes are the same colour.
You must show your working.
72 exam-style questions on Edexcel GCSE Maths Conditional Probability. Each one has a worked solution and a mark scheme showing where the marks go.