There are 20 counters in a bag. 13 of the counters are red. 7 of the counters are blue. Two counters are taken at random from the bag.
Work out the probability that one counter of each colour are taken.
You must show your working.
72 exam-style questions on OCR GCSE Maths Conditional Probability. Each one has a worked solution and a mark scheme showing where the marks go.