### Cube Net

How many tours visit each vertex of a cube once and only once? How many return to the starting point?

### Binary Sequences

Show that the infinite set of finite (or terminating) binary sequences can be written as an ordered list whereas the infinite set of all infinite binary sequences cannot.

### Binomial Coefficients

An introduction to the binomial coefficient, and exploration of some of the formulae it satisfies.

# Groups of Sets

##### Stage: 5 Challenge Level:

The equation $a*x=b$ has solution $x=a^{-1}*b$.