University of Cambridge
University of Cambridge: Nrich: Up and Down Stairs
Work with this cube problem and see if you can find a pattern. Then you can check your solution with solutions already submitted.
Shodor Education Foundation
Shodor Interactivate: Triangle Explorer
This applet gives you practice finding the area of a triangle. Great place for students to "discover" how you find the area of a triangle. Directions are just a click away. [Requires Java.]