## Partial Product

Imagine you're at a store that lets you pull products apart and pay for as much or as little of them as you want. What will your total grocery bill be for these three items?

If a student has no idea where to start, you can prompt her to list a price that sounds fair to her for the three sodas or, failing even that, a price that seems unfair to her. (You're basically asking her to give a wrong answer. It's a lot easier to give wrong answers than right answers because there are a lot more of them.)

You'll find students who divide all the way down to the unit rate (ie. each egg costs 19 cents) and then multiply back up. You may also find students who set up a proportion, which will disguise the unit rate in an interesting way.

You'll find students who set up different but equivalent unit rates. (ie. 19 cents per egg and .05 eggs per cent.) You'll find students who set up different but equivalent proportions.

One of your many challenges during this activity will be to select students to show work that highlights a) the different ways to find the unit rate, b) the different ways to set up the proportion, c) the equivalence within those methods, and d) the equivalence between those methods (ie. ask your students to help you find the unit rate within the proportions).

The Goods

Partial Product

Featured Comment

I’m with Christopher and, I think, Dan here: Toss it out with the understanding that students can use any method that makes sense to them. Then not only share those methods but compare them to see why they yield the same result. Love the word “catharsis” in this context.

## Redesigned: John Scammell

So John Scammell uploaded this #anyqs, which captured an interesting moment. In his tweet, he wrote, "When I was a kid, I'd grind other kid's pencils down to nothing."

Some things I'd like to accomplish in the redesign:

1. Get the camera lens parallel to the pencil, an angle that makes it easier to see the length changing.
2. Convey to the student visually what John wrote in his tweet: that this pencil is about to get ground down to nothing.
3. Postpone the pencil measurements until the second act. The moment where John measures the pencil is useful and necessary but the first act (the #anyqs) should focus exclusively on curiosity and context. The math introduces itself later in act two to help resolve that curiosity.

Act One

Act Two

Act Three

The Goods

## Dan Anderson’s Mathematical Story

Frameworks are inherently limiting. The more guidelines you specify, the more material you exclude, some of which can be very good. Frameworks are great, though, because they make implementation easy. I know what happens in the first, second, and third acts of a mathematical story, so it'd be a simple matter to use Dan Anderson's lesson in the classroom — no lesson plan or handout required.

## [WCYDWT] Russian Stacking Dolls

2011 May 15: Major updates on account of useful critical feedback in the comments.

Let's see how well the storytelling framework holds up.

The Goods

Act One

Play the question video.

Ask your students what question interests them about it. Take some time here. This is the moment where we develop a shared understanding of the context. If a student has some miscellaneous question to ask or information to share about the dolls, encourage it. That isn't off-task behavior. This task requires that behavior.

Then ask them to write down a guess at how many Russian dolls they think there are. Ask them to write down a number they think is too high and too low.

Act Two

After you show them the first set of two dolls, ask them how big they predict the third will be. As one of the commenters mentioned, they need to discover the fact that these guys aren't decreasing by a fixed amount every time, that a new model is necessary.

Once they have this new model in mind, they'll keep applying it until they reach a doll height they think is impossibly small.

Act Three

That task isn't going to win anybody a Fields medal. As students finish, ratchet up the demand of the task with this sequel. Say:

I need you to design me a doll that's as tall as the Empire State Building and is made up of 100 dolls total. Tell me everything you know about that doll.

Host a summary discussion of the activity. At this point you've identified different solution strategies around the room. Have those students explain and justify their work to their peers. Everyone is accountable for understanding everyone else's strategy.

Then show them the answer video:

Find out whose guess was closest.

[h/t @baevmilena who gave me the idea when I met her in Doha.]

## The Three Acts Of A Mathematical Story

2013 May 14. Here's a brief series on how to teach with three-act math tasks. It includes video.

2013 Apr 12. I've been working this blog post into curriculum ideas for a couple years now. They're all available here.

Storytelling gives us a framework for certain mathematical tasks that is both prescriptive enough to be useful and flexible enough to be usable. Many stories divide into three acts, each of which maps neatly onto these mathematical tasks.

Act One

Introduce the central conflict of your story/task clearly, visually, viscerally, using as few words as possible.

With Jaws your first act looks something like this:

The visual is clear. The camera is in focus. It isn't bobbing around so much that you can't get your bearings on the scene. There aren't any words. And it's visceral. It strikes you right in the terror bone.

With math, your first act looks something like this:

The visual is clear. The camera is locked to a tripod and focused. No words are necessary. I'm not saying anyone is going to shell out ten dollars on date night to do this math problem but you have a visceral reaction to the image. It strikes you right in the curiosity bone.

Leave no one out of your first act. Your first act should impose as few demands on the students as possible — either of language or of math. It should ask for little and offer a lot. This, incidentally, is as far as the #anyqs challenge takes us.

Act Two

The protagonist/student overcomes obstacles, looks for resources, and develops new tools.

Before he resolves his largest conflict, Luke Skywalker resolves a lot of smaller ones — find a pilot, find a ship, find the princess, get the Death Star plans back to the Rebellion, etc. He builds a team. He develops new skills.

So it is with your second act. What resources will your students need before they can resolve their conflict? The height of the basketball hoop? The distance to the three-point line? The diameter of a basketball?

What tools do they have already? What tools can you help them develop? They'll need quadratics, for instance. Help them with that.

Act Three

Resolve the conflict and set up a sequel/extension.

The third act pays off on the hard work of act two and the motivation of act one. Here's act three of Star Wars.

That's a resolution right there. Imagine, though, that Luke fired his last shot and instead of watching the Death Star explode, we cut to a scene inside the Rebellion control room. No explosion. Just one of the commanders explaining that "the mission was a success."

That what it's like for students to encounter the resolution of their conflict in the back of the teacher's edition of the textbook.

If we've successfully motivated our students in the first act, the payoff in the third act needs to meet their expectations. Something like this:

Now, remember Vader spinning off into the distance, hurtling off to set the stage for The Empire Strikes Back. You need to be Vader. Make sure you have extension problems (sequels, right?) ready for students as they finish.

Conclusion

Many math teachers take act two as their job description. Hit the board, offer students three worked examples and twenty practice problems. As the ALEKS algorithm gets better and Bill Gates throws more gold bricks at Sal Khan and more people flip their classrooms, though, it's clear to me that the second act isn't our job anymore. Not the biggest part of it, anyway. You are only one of many people your students can access as they look for resources and tools. Going forward, the value you bring to your math classroom increasingly will be tied up in the first and third acts of mathematical storytelling, your ability to motivate the second act and then pay off on that hard work.

Related

1. I gave this post a try a year ago.
2. Also, Breedeen Murray has a lot of useful things to say about storytelling, though I can't endorse her enthusiasm for "confusion."

2011 Dec 26: The Three Acts of a (Lousy) Mathematical Story is also on the syllabus.

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