Key stage 3 lesson where students learn about writing ratios in their simplest form using the highest common factor. As learning progresses students work with ratios involving time, metric units and currency notation.

The start of the lesson recaps scale drawings. The plenary challenges students to link area with simplifying ratios.

**Differentiated Learning Objectives**

- All students should be able to write a ratio in a simpler form using a common factor.
- Most students should be able to write a ratio in its simplest form using the highest common factor.
- Some students should be able to use equivalent ratios to solve problems involving currency.