An environmental protection agency monitors dissolved lead levels in a major river basin to assess the impact of industrial runoff. The table below shows the results of water quality analyses conducted by the agency in 2018 and 2023.
| Year | Total water samples analyzed | Percentage of samples exceeding the lead safety threshold (%) |
|---|---|---|
| 2018 | 12,400 | 3.5 |
| 2023 | 28,500 | 1.2 |
Calculate the decrease in the absolute number of water samples that exceeded the lead safety threshold between 2018 and 2023.
45 exam-style questions on OCR A A Level Biology Analysis. Each one has a worked solution and a mark scheme showing where the marks go.