There are some red counters and some blue counters in a bag.
The ratio of red counters to blue counters is 3:1.
Two counters are removed at random.
The probability that both the counters taken are blue is 120\displaystyle \frac{1}{20}201
Work how many counters were in the bag before any counters were removed.
28 exam-style questions on Edexcel GCSE Maths Probability Equation Questions. Each one has a worked solution and a mark scheme showing where the marks go.