Browsing around in my blog links, I found this:
Try it for yourself, and then:
- Can you explain how it works?
You will have to use a little algebra. If you were at my pre-algebra workshop, this will be like the “Choose a number” problem.
- Can you explain why this puzzle will not work next year?
What would you change to make it work in some year other than 2007?
- Can you make up a problem like this?
Or can your students?
And if you get stumped, the answer is here.