I'm looking to make a database of some math problems. I'm a secondary teacher and LOVE interesting problems to add to my bank. I'm looking for all kinds of problems, not just Algebra. Anything 6-12.
Here are some of my favorites:
Wine/water mixing problem - Wikipedia, the free encyclopedia
The String Around the Earth Problem .........
Connected Mathematics 2
Basically, problems that have interesting/surprising results, multiple ways to solve them, etc.
What are some of your favorites?