Finding a quantity given a percentage (or fraction) is a useful skill yet considered to be an extension topic for year 8. I thought I could give it a go but set the scene, so-to-speak, without the oft-used context of shopping and sales.
Enter the Vitruvian Man. Wikipedia has a good image and brief explanation of this drawing by Da Vinci interpreting ideal (hu)man proportions according to Vitruvius. Wikipedia also provides a list of these proportions.
My ‘hook’ question to the class was “How do forensic scientists figure out the height of victims given minimal data?”
I showed and explained the Vitruvian Man. We even managed to do a quick revision of properties of squares and how this was used in the drawing. Anyway, here’s how I used this “tool”.
- Divide the class into pairs (or small groups).
- For each pair, give a card which showed one of the proportions (e.g. 1/4 of height = shoulder width) as well as a measuring tape
- They take the fractional measurement of their partner, i.e. the item to the right of the equation, e.g. shoulder width
- Demonstrate how to calculate the height given a known percentage (or fraction); in my example, multiply each side of the equation by 4
- Finally, measure the actual height and compare to the calculated height
- How do the actual and calculated height compare?
- What are the reasons for differences?
- Why multiply both sides (make a point to mention working with Algebra and equations)?
The class really enjoyed the activity and didn’t really mind the ‘maths’ at all. Given that this class is deemed below-average, the level of engagement was good. The students – all girls – already associate percentages with sales but, for most if not all of them, this is the first time they’ve associated it with the human body. I know that I will use the Vitruvian Man again.
This was a lively lesson with talking and standing up and discussing. This isn’t every teacher’s cup-of-tea but it suits me just fine.