Whether you use this with a class or not, I promise you that you will never read a description of a math lesson that amuses you more than Matt Vaudrey‘s description of his Mullet Ratio Activity.
Note: I tagged this 10-3. I know it’s not a currency exchange ratio. It’s better than that. It would also fit in 20-2 (Foundations 11).
WNCP Orchestrated Experiences for High School Math 