Stage: 4 Challenge Level: 
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?
Place value. epsilons. alphas. Manipulating algebraic expressions/formulae. Factorisation (algebraic). Number bases. Creating expressions/formulae. Mathematical reasoning & proof. Difference of two squares. smartphone.
Published July 1997.
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