There also exists a GIANT holiday box of Smarties that weighs in at 430 g.

What questions come to mind?

How many Smarties? How much would that cost?

Let's tackle the second question first. What do we need to know? The cost per gram or the cost per Smartie. Collect some data!

They should get something similar to this:

The slope would give them the cost per gram. My equation was cost = 0.0215(mass) so for a box weighing in at 430 g should cost approximately $9.25.

Alternatively you could look at the cost per Smartie. We need to know the number of Smarties in each different size box.

Students can count the number of Smarties in each size box and then determine the cost per Smartie with a graph or a table:

Hopefully students make the connection that the cost per Smartie is the slope of the graph.

My equation was cost = 0.0226(number of Smarties). We can use that equation to determine the approximate number of Smarties you would get for $9.25. A little linear equation solving yields 409 Smarties. Now I have to wait until December to verify my work!

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