Some are simple and make good warm-up activities. Others involve substantial problem solving. Print out a copy of some of the problems and try them. Solutions are not available at the website. You will have to request the solutions via mail.
New puzzles appear each month.
A challenge problem is presented each week in the form of a story. Students are invited to send in their solutions and can also find out how other students solved the challenge problem. Bookmark this site and try it with your students. This website provides a good collection of interactive puzzles and games for students to solve. This site is best used by grades 6 and up.