If there are nine people in a room and every person shakes hands exactly once with each of the other people, how many handshakes will there be? How can you prove your answer is correct using a model ...

The first time I was allowed to travel beyond the Iron Curtain and visit the West was in 1980. I ventured from Hungary to New York for the International Toy Fair, where a puzzle I had invented was ...

This video is no longer available. Sai Charan Kintali carries so many puzzle cubes with him during the day at Irving Middle School in Springfield, Virginia, he keeps them in a special black case in ...