This week we get to the origins of the Decimal Institute.

One Thursday evening, I was sitting around thinking about the Khan Academy knowledge map, trying to put my finger on the exact argument that I wanted to make about why the decimals-before-fractions thing was so deeply disturbing to me. I was trying to formulate an argument that math teachers would find convincing.

I settled on this.

But seriously, what is your explanation for why one tenth is the best fraction to study first?

— Christopher (@Trianglemancsd) September 27, 2013

Is there ANYTHING in a child’s everyday life that gets cut into tenths? Anything at all? — Christopher (@Trianglemancsd) September 27, 2013

Twitter settled on money (see week 2) and pizza. I contended (and still do) that a 10-slice pizza is a rare beast. I may have overstated their rareness in my sign off that night:

You all go enjoy your mythical 10-slice pizzas, OK?

— Christopher (@Trianglemancsd) September 27, 2013

Which I will assume that you are splitting equally with 9 unicorns.

— Christopher (@Trianglemancsd) September 27, 2013

And slicing with your light sabers.

— Christopher (@Trianglemancsd) September 27, 2013

Yes, I admit that this was an overstatement. But pizza slicing is just the thing we need to lighten the mood this week, so let’s investigate together the various ways pizzas are in fact cut.

For example, here are instructions for a 10-slice pizza. (Or are they? In any case, tip o’ the chef’s cap to Kate Nowak for the find)

And here is the closest thing I could find to light-saber pizza cutting (with thanks to Chris Robinson).

And here is a machine whose sole purpose is precision cutting of pizzas into 7 slices (props to Malke Rosenfeld for the find).

To finish my story, the Decimal Institute was born the following morning. My Twitter conversation made clear that not all math teachers were buying my argument made 140 characters at a time. So I offered to talk about these ideas in a (MUCH) longer format.

This week, let’s slow things down and have a bit of fun.

Our challenge as a group is to find the complete set of numbers into which pizzas are (or have been) equally partitioned.

For example, I have provided evidence in this post that 8 (the laser cutter) and 7 are in this set. I have not provided evidence that 10 is (did you watch that video carefully?).

Our standards for evidence are high. Photographs, videos and original documents are acceptable. Clip art for middle school textbooks are not.

We will collect and discuss on Canvas. I will curate and share what we find here on the blog in a week or so.

Go!

## Update

Leslie Billings asks:

Does it matter what shape the pizza is before cutting? ie Circular vs Rectangular? Or some other shape?

I feel comfortable leaving these issues to the community of interested parties.