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Team Selection Test Selection Test #0j93

Team Selection Test Selection TestHard

From module Functional Equations II

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Understand the scale
Scale 0.5: Easiest math competition problems, often solvable even for early middle school students without experience. 1: Problems strictly for beginners, often at a moderate middle school level. 1.5: Problems for stronger beginner students, on the level of the middling problems in most middle school contests. 2: For motivated beginners, harder questions from the previous categories. 2.5: More advanced beginner problems, hardest questions from previous categories. 3: Early intermediate problems that require more creative thinking. 3.5: Tougher early intermediate problems that consistently stretch into higher-level creative thinking or conceptual knowledge. 4: Intermediate-level problems. 4.5: Upper intermediate problems approaching the upper bound for non-invitational sprint math competitions. 5: More difficult AIME problems or simple proof-based Olympiad-style problems. 6: High-level AIME-styled questions or introductory Olympiad-level questions. 7: Tougher Olympiad-level questions, may require more technical knowledge. 8: High-level Olympiad-level questions. 9: Expert Olympiad-level questions. 9.5: The hardest problems appearing on Olympiads which the strongest students could reasonably solve. 10: Historically notorious problems, generally unsuitable for even very hard competitions because they are exceedingly tedious, long, and difficult.
Functional Equations

Problem

Find all real-valued functions ff defined on pairs of real numbers, having the following property: for all real numbers a,b,ca, b, c, the median of f(a,b)f(a, b), f(b,c)f(b, c), f(c,a)f(c, a) equals the median of a,b,ca, b, c. (The median of three real numbers, not necessarily distinct, is the number that is in the middle when the three numbers are arranged in non-decreasing order.)

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