Friday 13 March 2015

MFM2P - Day 28 (More SA & V of prisms and cylinders)

Today's warm up is our first math talk. And I'm not there : (  They will be doing 12 x 15 without a calculator. I want to see as many strategies as possible. I am always amazed at how many kids will actually draw 12 groups of 15 dots of 15 groups of 12 dots and either count or add up the result. I was sure I had a picture from a previous class that had done this math talk, but I can't find one. Here are some of the strategies that I might see:

My students always come up with ones that I don't think of, which is the beauty of doing math talks. All students see that there are multiple ways of getting to an answer. Regardless of whether you are the top student or one who is struggling, you found a way and can learn from others. If you are not familiar with math talks, you might want to check out Jo Boaler's work and the YouCubed website.

As I didn't know quite how far my students would get in my absence yesterday, I left some really boring worksheets for them to practice calculating surface area and volume of prisms and cylinders. As much as I like to keep my students engaged and don't think these worksheets will necessarily do that, I think some will need the practice and my substitute teacher will need something concrete for them to work on. Working with triangular prisms is especially tricky for many of my students so this will hopefully help them work out the kinks in their thinking.

I also left them this 3-act to work on.

I hope I am "tricking" them into remembering that the sides of a cylinder come from a rectangle while doing some hands-on work. Thank you, Dan Meyer, for again helping me make my class better.


  1. I've been doing SA of triangular prisms with 6th grade and it has been really tough getting kids to recognize the 2D shapes or correctly attribute the right measurement with the right side. Eventually, we found that each of the rectangles lengths are all the depth of the prism. Each rectangle is found my multiplying this depth by each side of the triangle. While the logic is sound, I fear that they'll easily forget this. Tough stuff.

    1. Agreed! I will likely take Toblerone bars in when we look at triangular prisms again. And they won't be allowed any chocolate until they correctly calculate the surface area!