Saturday, April 26, 2014

111: Dirt Triangle

Taken from David Cox, changed just a little:

While I was out, I left a few distance/rate/time problems for students to solve.  Upon my return, I was asking students about the problems and many students had similar responses.
S:  "The Dirt Triangle."
Me:  "?"
S:  "Look, Mr. Cox it's like this...
"...You cover up the one you're looking for and if the other two are next to each other, you multiply.  If one is above the other, you divide."

Me:  "Really? That's strange.  I never learned the Dirt Triangle. I learned ... The Turd Triangle

S1: "No, that won't work. That's not what he told us."
S2: "He said it didn't matter how we wrote it."
Me: "So which is it; does one work or are they the same?  Make your case and be ready to defend it."


  1. As long as I don't have to be some kind of Will Hunting and actually understand one of the most basic and intuitive equations possible, either one works. But if I can't spend a few class periods making some kind of construction paper triangle glued onto posterboard and present my discovery to the class, I still probably won't remember the turdriangle.

  2. Here is a perfect example of the difficulty we have with definitions of words in English and in Math. Hours/mile is indeed a rate, but it is not *the* rate that kids are assuming you mean. If you are working with 6-7-8th graders, the trD triangle does NOT work, unless you are consciously upending their understanding of the basic terms *with* their full co-operation ... and that is counterproductive at this point.