Jamuna has a circular piece of paper. She is trying to locate its centre. Amina gives her a suggestion. She follows the instructions and is thrilled to find that it works. Can you guess what Amina told her?                    [Page No. 93]

Amina told her to fold the circular paper in half so that the boundary of the circle falls exactly on itself, and then open it out. The crease that appears is a line of reflection symmetry of the circle, and every such line is a diameter, so the crease must pass through the centre. One crease alone is not enough, though, because the centre could be anywhere along it.

So Amina asked her to fold the paper a second time in a different direction, again making the edge overlap itself. This gives a second diameter. The point where the two creases cross is the centre of the circle, since the centre is the one point that lies on every diameter, and two different diameters meet at exactly one point.