Priya wants to find an estimate for the number of birds in a wood.
She catches 100 birds and puts a ring on each of their legs.
She then releases the birds back into the wood.
A week later, Priya catches another 80 birds.
20 of these birds have rings on their legs.
Work out an estimate for the number of birds in the wood.
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.