I am a fan of this type of question, as a matter of fact, I used this one picture as the basis for a whole Ministry of Education project called “Loving the Math, Living the Math”.
My feeling was this: something is “out of whack” with the smallest cup. That “something” is the fact that it is disproportionately priced. You get the upsell every time. It is “much cheaper”, so they tell you, to buy the larger cup. Proportionally, that is always true. The price per unit (let’s use the Litre) goes down as the cup size goes up.
Kids sniffed this out. They wanted to set the price at around $2.25 for the smaller cup. They reasoned that the materials cost was something like 12 cents per cup (I recall them doing some research).
They were even more outraged when they looked up some prices on websites, and found that if you buy from stores like Costco, or Walmart, you can often get the price under $1/Litre of pop.
Here is an ad we found in an old newspaper from 1980.
Try comparing the 1980 Shopper’s unit rate to the Cineplex 2014 unit rate. What do you notice, wonder?
Here are places I think this sort of inquiry could lead us. These are some possible points of departure.
-find the cheapest price for pop you can. Use apps like Flipp, or maybe flyerland.ca.
-look at other things you can drink, like juice or milk. How are their prices in comparison?
-how much is water per litre in bottles? Why is it so cheap?
Finally, most devastatingly: look up the price to get water from the tap at home. Compare. Order all the prices from least to greatest.