### Diophantine N-tuples

Can you explain why a sequence of operations always gives you perfect squares?

### DOTS Division

Take any pair of two digit numbers x=ab and y=cd where, without loss of generality, ab > cd . Form two 4 digit numbers r=abcd and s=cdab and calculate: {r^2 - s^2} /{x^2 - y^2}.

### Sixational

The nth term of a sequence is given by the formula n^3 + 11n . Find the first four terms of the sequence given by this formula and the first term of the sequence which is bigger than one million. Prove that all terms of the sequence are divisible by 6.

# Balance Point

##### Age 14 to 16 Challenge Level:

Students need to be familiar with the principle of moments.
The problem called "Inside Outside" will help with this.

This problem requires careful systematic working and the utilisation of symmetry to reduce the arrangements to be tested to a manageable number (12).