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Romania Junior TST 2021 Day 3 P4

Source:

June 7, 2021
combinatoricsSetsOperationsromaniaRomanian TST

Problem Statement

Let MM be a set of 1313 positive integers with the property that  mM, 100m999\forall \ m\in M, \ 100\leq m\leq 999. Prove that there exists a subset SMS\subset M and a combination of arithmetic operations (addition, subtraction, multiplication, division – without using parentheses) between the elements of SS, such that the value of the resulting expression is a rational number in the interval (3,4)(3,4).