## Monday 3 March 2014

### MFM2P - Day 19 Filing Cabinet

Day 19
Today was File Cabinet day! That is Andrew Stadel's (@mr_stadel) fantastic File Cabinet 3-act - his blog post with links to the videos is here

This is the first time this year that these grade 10 applied students have done any surface area/volume calculations.

Here is the set up:

In the video we see Andrew placing numbered Post-it notes on the filing cabinet - 12 for the first row, and up to 24 for the second row, then the video stops. So, how many to cover the filing cabinet?  I asked them what they needed to know to answer this.
Student: "The dimensions of the filing cabinet."
Me: "Great.  What else?"
Another student: "The size of the sticky note."
Me: "Okay - anything else?"
They thought they were good to go so I gave them the handout.  Their first job was to estimate how many Post-it notes it would take.  The guesses ranged from 200 to 6000! As I circulated and talked to them about their estimates and what the first step in calculating the number of Post-it notes would be, many asked an additional question: "Is he covering all the sides?" or "Is he covering the top?" or "Is he covering the bottom?".  Many also revised their guesses based on my answer. Good. I found it really helpful to take a box in which I store pencils around the room with me for these discussions.

Many students said that they didn't have enough information to calculate the area of the top of the filing cabinet. It became clear to them that they could when we looked at the length, width and height of the box. They did great work. Some groups had several different answers so I got them to compare and figure out which was correct. Every group did this and chose the right answer and made corrections to errors in the other solutions. (Yay!) Every group agreed on the same answer so we played the Act 3 video and, well, I don't want to ruin it for you, so go ahead and calculate it yourself and see how you do : )

I was surprised that they did not have any trouble understanding that they needed to divide the total surface area by the area of one Post-it note. That was intuitive to them.

Next, we extended:

There were questions.
"All the walls? What about the windows?"
"Do we cover the blackboards?"
"What about the cabinet at the back?"
I suggested that the problem would be simpler if we did cover everything (hypothetically - we are not crazy like Andrew Stadel!), but that we should take into account the weird jogs in the walls and the cabinet at the back.

Some students were reluctant to get up and start measuring, but with a little encouragement, we got all the walls measured. They were not interested in agreeing on units so some used imperial and others metric.

They were busy calculating the surface area of the walls when the bell rang. To be continued tomorrow...