Ten squares form regular rings either with adjacent or opposite
vertices touching. Calculate the inner and outer radii of the rings
that surround the squares.

If a is the radius of the axle, b the radius of each ball-bearing, and c the radius of the hub, why does the number of ball bearings n determine the ratio c/a? Find a formula for c/a in terms of n.

The Dodecahedron

Age 16 to 18 Challenge Level:

A and B are the centres of two opposite faces of a regular solid dodecahedron.

What is the shortest distance between A and B on the surface?