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Bundeswettbewerb Mathematik 1976 Problem 1.3

Source: Bundeswettbewerb Mathematik 1976 First round

September 11, 2022
treerationalalgebra

Problem Statement

A set SS of rational numbers is ordered in a tree-diagram in such a way that each rational number ab\frac{a}{b} (where aa and bb are coprime integers) has exactly two successors: aa+b\frac{a}{a+b} and ba+b\frac{b}{a+b}. How should the initial element be selected such that this tree contains the set of all rationals rr with 0<r<10 < r < 1? Give a procedure for determining the level of a rational number pq\frac{p}{q} in this tree.