MathDB
Iran MO 2nd round 2016

Source: 2016 Iran MO 2nd round p3

June 9, 2017
combinatoricsIran

Problem Statement

A council has 66 members and decisions are based on agreeing and disagreeing votes. We call a decision making method an Acceptable way to decide if it satisfies the two following conditions:
Ascending condition: If in some case, the final result is positive, it also stays positive if some one changes their disagreeing vote to agreeing vote. Symmetry condition: If all members change their votes, the result will also change.
Weighted Voting for example, is an Acceptable way to decide. In which members are allotted with non-negative weights like ω1,ω2,,ω6\omega_1,\omega_2,\cdots , \omega_6 and the final decision is made with comparing the weight sum of the votes for, and the votes against. For instance if ω1=2\omega_1=2 and for all i2,ωi=1i\ge2, \omega_i=1, decision is based on the majority of the votes, and in case when votes are equal, the vote of the first member will be the decider. Give an example of some Acceptable way to decide method that cannot be represented as a Weighted Voting method.