None of the following puzzles has a trick answer, or unwarranted assumptions. They are arranged approximately in order of difficulty; the first few can be done by elementary school children, but they may need to be taught how to think. I tried to include a wide variety of types of puzzles, so that each would teach a new lesson in finding creative solutions by breaking a variety of kinds of mental blocks. Moreover, most of them can be solved mentally by using a judicious point of view.
"This archive is designed as a resource for enriching your math courses and nurturing your interest and talent in mathematics! Each Math Fun Fact is a math puzzle or short article that contains a cool mathematics idea. You'll can learn about the mathematics of things like card shuffling to poker to computer vision to fractals to music, just to name a few. This makes great enrichment material for gifted math students or problem-solving groups."
This site is a free resource maintained by Jefferson Lab in Newport News, VA. It contains resources, lessons, activities, games, puzzles, etc. for teachers and students.