There are some green marbles and some yellow marbles in a jar.
The ratio of green marbles to yellow marbles is 4:14:14:1.
Two marbles are removed at random without replacement.
The probability that both the marbles taken are yellow is 135\displaystyle \frac{1}{35}351.
Work out how many marbles were in the jar before any marbles were removed.
43 exam-style questions on OCR GCSE Maths Probability Equation Questions. Each one has a worked solution and a mark scheme showing where the marks go.