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Minimum and maximum value of \frac{a}{b}+\frac{c}{d}

Source: XIX Olimpíada Matemática Rioplatense (2010)

July 22, 2011
inequalitiesnumber theory unsolvednumber theory

Problem Statement

Find the minimum and maximum values of S=ab+cd S=\frac{a}{b}+\frac{c}{d} where aa, bb, cc, dd are positive integers satisfying a+c=20202a + c = 20202 and b+d=20200b + d = 20200.