National Council of Teachers of Mathematics
The Math Forum: Calculation Tips & Tricks: Multiplication Tips
Find tips for multiplying by 5, 9, and 11, and learn how to solve math problems without a calculator. This site includes explanations and examples for gifted children and teachers wanting to challenge their students.
Other
Problems in the Points Contest of Ko Mal
Learn about the annual KoMal competition in mathematics, physics, and information technology, and challenge your ability to solve problems involving advanced algebra, logic, and other related topics through the tests provided at this site.
Braingle
Braingle: Probability Brain Teasers
Check out the variety of probability brain teasers at this site, which you can sort by popularity and difficulty.
Braingle
Braingle: Math Brain Teasers
Check out the variety of math brain teasers at this site, which you can sort by popularity and difficulty.