That is because your students don't understand algebra. Why don't you try teaching it to them?
A student of algebra would NEVER attack this problem with assumption (actually, I think the word is "guessing"). That is the whole point of teaching algebra. So that students learn to think rather than guess.
On May 27, 2013, at 10:38 AM, Richard Strausz <Richard.Strausz@farmington.k12.mi.us> wrote:
> And here is another Wayne. My students know the formulas for surface area and volume, but they often make false assumptions. I like this: > > http://blog.mrmeyer.com/?p=14118 > > Richard