Beth wants to estimate the number of frogs in a lake.
She catches a sample of 90 frogs, marks them and puts them back in the lake.
Later that day, in a second sample of 90 frogs, she finds that 15 of them are marked.
Work out an estimate for the number of frogs in the lake.
Write down any assumptions you have made.
87 exam-style questions on WJEC GCSE Maths Capture Recapture. Each one has a worked solution and a mark scheme showing where the marks go.