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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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Novemberish

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.

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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?

What a Joke

Stage: 4 Challenge Level: Challenge Level:2 Challenge Level:2

If you rearrange the expression you will notice that AHHAAH has to be divisible by HA.

422442 can be written as 42 x 10001 + 24 x 100.
AHHAAH can be written in the same way...

10001 is not a prime number.