I've been reading Dan Meyer's blog for a while now. He's a big supporter of asking for wrong answers but he doesn't just ask for them when nobody knows the answer. He asks for wrong answers all of the time. I tried the technique last week before asking for the correct answer. I was blown away by the quality of wrong answers I was getting. Here's the graph we looked at:
We had just calculated the slope of the blue to be -1. I added the red line to the graph and before asking what its slope could be I asked for what its slope can't be. I originally expected a lot of ridiculous answers. I was pleasantly surprised.
Here are some of the responses I received:
- Can't be negative 1, since the slope is different from the blue line (nice segue into slopes of parallel lines)
- Can't be zero since it's not a horizontal line
- Can't be -1000 (a little silly but nailed down that our solution needed to be between -1 and 0)
- Can't be undefined