Estonian Math Competitions 2005/2006
Source: Seniors Problem 4
July 30, 2008
algorithmgreatest common divisorcombinatorics unsolvedcombinatorics
Problem Statement
Martin invented the following algorithm. Let two irreducible fractions and be given as inputs, with the numerators and denominators being positive integers. Divide and by their greatest common divisor and obtain and , respectively. Similarily, divide and by their greatest common divisor and obtain and , respectively. After that, form a new fraction \frac{a_1b_2 \plus{} a_2b_1}{t_1b_2}, reduce it, and multiply the numerator of the result by . Martin claims that this algorithm always finds the sum of the original fractions as an irreducible fraction. Is his claim correct?