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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}.

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Latin Numbers

Can you create a Latin Square from multiples of a six digit number?

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2-digit Square

A 2-Digit number is squared. When this 2-digit number is reversed and squared, the difference between the squares is also a square. What is the 2-digit number?

Novemberish

Age 14 to 16 Challenge Level:

eleven.

(a) A four digit number (in base $10$) $aabb$ is a perfect square. Discuss ways of systematically finding this number.
(b) Prove that $11^{10}-1$ is divisible by $100$.