Sarah wants to find an estimate for the number of fish in a pond.
She catches 40 fish from the pond and marks each one with a tag.
She then returns the fish to the pond.
A week later, Sarah catches another 50 fish.
4 of these fish are marked with a tag.
Work out an estimate for the number of fish in the pond.
Write down an assumption you have made.
20 exam-style questions on OCR GCSE Maths Capture Recapture. Each one has a worked solution and a mark scheme showing where the marks go.