Geometry – Day 66 – Review Period

Come for:

  1. A rockin’ review set.

Stay for:

  1. An inglorious end to the stopsign project.
  2. A completely gratuitous review of text messaging dictionaries.
  3. An awesome probability problem (for Tony and the other probability ‘shippers) we cut out for the sake of time.
  4. The first day of State Week! (Far less popular than Phobia Week, I’m afraid.)


  1. None


Slide Deck

  1. Kentuckian, Minnesotan, Floridian, Marylander, Idahoan
  2. Discuss here my own personal problems with the stop sign project. Too tall. Even for my freak height.
  3. So I just measured the side length.
  4. [N.B. A year into this digital projector experiment and it still freaks me out how fun it is to toss up any photo I want, whether for illustrative, instructional, or completely pointless purposes.]
  5. Then I pulled a nerd move. I took a scale stop sign from wikipedia. Measured pixels and used a basic proportion to figure out the last measurement.
  6. We’ve talked about basketball right. Divide the class in two. Put up a question. They show all their work. (Make ’em turn in all their chickenscratch at the end and then toss it.) They stand up when they have an answer. If they get it right, they get two shots. Scoring can be kind of fun to come up with yourself. They can’t answer again until their whole team has shot. No passing answers.
  7. Translating words to symbols.
  8. Next year match this slide with one showing the accurately measured triangles for reference. (i.e. “Ohhh, it was acute.”)
  9. Talk about how the guy is shortchanging you by $43. Fun question.[N.B. Never got around to it in either section, though. With basketball review (and in general) you’ve gotta overplan. I just wish I had tossed this in the front forty.]

Notes & Revisions:

  1. Pull the swimming pool probability problem forward next year. (Slide #14)
I'm Dan and this is my blog. I'm a former high school math teacher and current head of teaching at Desmos. He / him. More here.


  1. Tony, I can’t pull a comment form up on your blog. So, anyway:

    I’d love a good probabilistic run-down of an episode of Deal Or No Deal if you felt like providing one. The first episode I saw, I pulled open my laptop at a friends’ house, fired up Excel, and punched in a formula for the suitcase’s expected value. I’d predict what the banker would offer, tell the teevee person when she oughtta take the money and when she should stand, and generally make a nuisance of myself among polite company.

    They were good times, but I could never predict the Banker’s strategy with sort of reliability or accuracy. Someone oughtta handle this, in any case.

    And fwiw, it’s pronounced “dee why dan.”

  2. I used Deal or No Deal as an example when I was a teaching assistant for regression courses. It turns out (and this was not my idea–I found it somewhere on a web site and I can’t find the site any more) that a regression model can predict the banker’s offer very well (R^2 in the high .90s) given an interaction term between the average of the remaining cases (expected value) and the round number (1 = first time the banker makes an offer, 2 = second time banker makes an offer, etc). The R^2 is so high that I think the banker basically uses an equation similar to the regression equation and then just adds in some random noise.

    P.S. I was at your OTF presentation this week–a lot of great stuff there (and here on your site)!

  3. Brian, you’re a tease, man. Hinting that the regression model exists is only gonna keep me searching.

    Thanks for the intro, anyway, and the link to your site, which has some fun stuff.

  4. Dan–I know the regression model that works, I just don’t remember where I learned it from. If offer = banker’s offer, round = round number and average = average of remaining cases, then a regression model of the form offer = b0 + b1*round + b2*offer + b3*round*offer will work really well (R^2 > .9). I can send you some data if you want to try it out.