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GM of set = GM of the GMs of all non-zero subsets

Source: Canadian Mathematical Olympiad - 1983 - Problem 5.

June 26, 2011
combinatorics proposedcombinatorics

Problem Statement

The geometric mean (G.M.) of kk positive integers a1a_1, a2a_2, \dots, aka_k is defined to be the (positive) kk-th root of their product. For example, the G.M. of 3, 4, 18 is 6. Show that the G.M. of a set SS of nn positive numbers is equal to the G.M. of the G.M.'s of all non-empty subsets of SS.