This activity comes from the awesome Michael Fenton. He also has a Desmos version of it which I posted on my website so that any absent students could do that version of the activity at home.

**Act 1**

I asked “What do you notice?”:Then I asked “What Mathematical questions do you have?”

I then presented them with the question I had chosen ahead of time to address the curriculum expectation “Create graphs and equations of linear relations” & asked for an estimate that was too high, too low & best estimate:

**Act 2**

I asked what information they would need in order to solve this problem & got answers such as . . . . . . so I gave them:

They went to their boards & solved. Some groups counted up the entire way using a table of values: Other groups determined a rate of charging that they used to multiply by the % charge left to go:These two groups above had some guidance along the way from me in terms of questioning the values they picked for the change in charge and the change in time; both groups reworked their solution at least once.

One group, with help from a discussion with me, created a proportion:This group had the proportion idea on their own but needed some guidance in how to set it up properly.

**Act 3**

Answer reveal:Michael does a great job of breaking down why the actual answer is so different from the models my students made here on his original blog post.

The following day we worked through this handout which forced them to create a graph & determine an equation for the relation.

And, as always, here is the folder with all the materials for this activity.

– Laura Wheeler (Teacher @ Ridgemont High School, OCDSB; Ottawa, ON)

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