Make a cube out of straws and have a go at this practical
Reasoning about the number of matches needed to build squares
that share their sides. How can the same pieces of the tangram
make this bowl before and after it was chipped? Use the
interactivity to try and work out what is going on! Look at this
image for a short while before turning away. Here is a Word
document containing the image. This image is taken from the
NRICH Mathematics Posters CD called "Exploring Squares"
published by Virtual Image. More details of this and the
"Exploring Circles" CD can be foundhere.