Where Can I Find Engaging Math Puzzles for Ages 12-18?

[Natasha1]

Does anyone know of a good website on maths puzzles, games, etc... which I could use in a class for an age group of 12-18 years old? (Even 20+)

Many thanks,

Nat

 

[shmoe]

http://www.cut-the-knot.org/index.shtml has some good material

I'm also a fan of the game set http://www.setgame.com/ for having some interesting related math problems ranging from counting to vector spaces over finite fields. Might be expensive to buy enough packs for a class though.