Maths Challenge
Maths challenge.net: Problem Solving Database
Need some challenging problem-solving work for your students in the following areas: Discrete, Geometry, Numbers, and Code Breaking? This is the place for an enormous database of problems aimed at high school age students. They are...
National Council of Teachers of Mathematics
The Math Forum: Classic Problems From the Dr. Math Archives
Several classics in the world of math are demonstrated on this Math Forum site. Clear explanations are given for each problem and links are included for extensions.