Stage: 5 Challenge Level: 
My phone number has seven digits: if the last four digits are placed in front of the remaining three you get one more than twice my number! What is the number?
Place value. Inequality/inequalities. Euclid's algorithm. Stage 5 - Reviewed 2012. epsilons. alphas. Diophantine equations. Mathematical reasoning & proof. Summation of series. Manipulating algebraic expressions/formulae.
Published September 1999.
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