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Voting power distribution (Posted on 2005-01-24) Difficulty: 4 of 5
The five owners of Plexus and Co. are voting on a very important decision (Top secret!). Each must vote for or against the decision. They don't necessarily own equal shares of the company, so they don't necessarily have equal voting power. For example, one person might have 5 votes and the other four have 1 vote each. However, it is distributed in a way that a tie is impossible. Obviously, everyone has positive voting power.

There are 2^5=32 different ways that the five people can vote (such as YYNNY, YNNYY, NNNNN, ...). Each way will result in favor or against the decision, depending on how the voting power is distributed.

There are 2^32 different combinations of the 32 outcomes, but not every combination is possible. For example, it is impossible for YYYNN to be in favor of the decision while YYYYN is against the decision, no matter how the voting power is distributed.

Out of the 2^32 different combinations, how many are possible, remembering that combinations where a tie is possible are not allowed?

  Submitted by Tristan    
Rating: 3.7143 (7 votes)
Solution: (Hide)
Let us assume that there are only these three rules limiting the possible combinations out of the 2^32:
1. If everyone votes nay, then the result is nay.
2. If a combination of votes is nay, then the opposite combination, where everyone votes in the opposite direction, is yea (and vice versa).
3. If a combination of votes is yea, then it will still be yea if anyone who voted nay changes to yea.

Because of the second rule, I only need to list 16 of the 32 voting combination. The other 16 combinations simply have the opposite results. "Y" stands for "yea" and "N" stands for "nay."

YYNNN  YNNNN  NNNNN
YNYNN  NYNNN
YNNYN  NNYNN
YNNNY  NNNYN
NYYNN  NNNNY
NYNYN
NYNNY
NNYYN
NNYNY
NNNYY
By rule 1, the result of the third column must be against. By rules 2 and 3 together, no more than one combination in column 2 can result yea. If one combination in column 2 did result in favor, then the voting power is distributed in such a way that one person's vote has complete control (like a distribution of {5,1,1,1,1}). When this is the case, we have no more freedom to change the results of the 10 combinations in column 1. There are five permutations of this voting power distribution.

The rest of the voting power distributions must result in nay for all of column 2. Following rules 2 and 3, there are only a few basic combinations of results possible.

In this list, each column after the first is numbered and represents one of the possible results of outcomes, excluding the permutations.

       1 2 3 4 5 6
YYNNN  Y Y Y Y Y N 
YNYNN  Y Y Y Y N N
YNNYN  Y Y N N N N
YNNNY  Y N N N N N
NYYNN  N N Y N N N
NYNYN  N N N N N N
NYNNY  N N N N N N
NNYYN  N N N N N N
NNYNY  N N N N N N
NNNYY  N N N N N N
The following list shows an example distribution for each of the 6 possible combinations of outcomes, and the number of permutations.
   example    permutations
1: 3,1,1,1,1  5
2: 4,2,2,2,1  20
3: 3,3,3,1,1  10
4: 3,2,2,1,1  30
5: 2,2,1,1,1  10
6: 1,1,1,1,1  1

Adding up all the permutations as well as the first 5 distributions counted, there are 81 unique voting power distributions. Since I found an example for each, my original assumption is correct, at least for the 5-owner case.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
SolutionMonotone functionsMath Man2013-07-28 22:00:57
answerK Sengupta2008-02-08 06:06:02
SolutionSolution?Dej Mar2007-11-17 00:40:24
Questionre: computer solutionDej Mar2007-11-16 10:54:50
re: Christmas CrackersCharlie2005-01-27 04:04:57
SolutionChristmas Crackerssassy2005-01-26 17:34:44
Diagrams?Gamer2005-01-25 20:41:28
re: ClarificationRichard2005-01-25 01:57:49
Solutionre: computer solutionCharlie2005-01-25 01:49:14
Solutioncomputer solutionCharlie2005-01-25 01:44:41
re: ClarificationDavid Shin2005-01-24 22:24:47
ClarificationDavid Shin2005-01-24 22:12:36
QuestionPerplexedRichard2005-01-24 21:56:37
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