Sometimes as a maths teacher, you strike gold. And often in the supermarket.
I called in quickly yesterday, on the hunt for some images to share with teachers that would provoke a discussion about unit rates. I didn’t buy anything, but I found something too good not to share.
The fruit & veg section is a good place to start. I wandered around, taking photos of lemons, oranges, and mandarins. And then I found this pair of images.
Finding the same product advertised at the same price but for different units felt like striking gold. So now I’m betting you have some questions. I did.
So I took some more photos. (The staff were watching me carefully by this point.)
An 8pk that weighs 560 grams, or 4 for 475 grams … what’s going on?
Now, this is going to feel quite unsatisfying because I don’t have a photo (I wasn’t paying $6.90 for eight kiwifruit, and I wasn’t going to break the seal on the packaging), but trust me when I say those 8pk kiwifruit were teeny tiny. Nowhere near the size of those individual beauties.
Where does this fit in the Australian Curriculum: Mathematics (AC:M)?
To be honest, ACMNA174 (Investigate and calculate ‘best buys’, with and without digital technologies) in v.8.4 always felt a little artificial to me — but not when presented with opportunities like this! In v9 this has been folded in the consolidating descriptor at the end of Number in Year 7: AC9M7N09 (use mathematical modelling to solve practical problems involving rational numbers and percentages, including financial contexts; …). But it is also relevant to many other descriptors in Number and Measurement, as well as connection throughout the Numeracy progression.
And how might you use it in class? I’d probably tell a story about how I’d been shopping for kiwifruit to put on my pavlova, and I couldn’t decide which was the better deal. Or something. I’d ask them what they noticed and wondered. Or, I could just show a formula, display the image, and ask students to calculate. The first is explorative and a little playful; the second far more directed. As to which is more effective, I encourage you to read Anna’s post for how a similar problem unfolded in her class.
When I encourage people to be creative, playful and explorative in their teaching, it inevitably brings out the detractors who extrapolate to mean that students won’t be learning anything. But good teaching is always carefully structured, even if it doesn’t look that way. It’s not simply a free-for-all. With practice, it’s not hard to inject a little more student engagement and interest into your lesson. It might just take a visit to the supermarket.
