# Selected topics in finite mathematics/Weighted voting

Weighted voting is a means of voting or pass (or fail to pass) a motion when the voters may have differing power.

## Objectives

[edit | edit source]Understand weighted voting and critical voters.

## Details

[edit | edit source]A weight is the number of votes that each participant is given and in order for a motion to pass, the number of in votes in favor of a decision must reach a quota.
With weighted voting systems there are two important types of voters, one who has veto power and a dummy voter. If one has **veto power**, their vote is required to pass or gail any motion, and a **dummy voter** has not influence in any part of the election.

**Unreasonable**: when it can't pass due to the fact that they pass and fail at the same time

**Reasonable**: when the motion either fails or passes

## Examples

[edit | edit source]Three entrepreneurs found a company together. But they all invest different amounts. One invests $20,000, another invests $30,000, and the third invests $40,000. Accordingly they own 20, 30, and 40 shares of stock in the company. In case of dispute, a decision is made based on stock, using the weighted voting system [45:20,30,40]. While each founder owns a different amount of stock, it turns out that their voting system is nothing more than a simple two-out-of-three majority.

## Nonexamples

[edit | edit source]## FAQ

[edit | edit source]## Homework

[edit | edit source]Describe the weighted voting system [9:5,4,3,2,2,1]. |

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In the weighted voting system [9:5,4,3,2,2,1], identify any voters with veto power and any voters that are dummies. |

Construct a weighted voting system in which everybody has veto power. |

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Construct a weighted voting system in which exactly half the voters have veto power. |

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Construct a weighted voting system in which exactly half the voters are dummies. |

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Construct three weighted voting systems which are equivalent to [67:24,24,24,24,3,1]. |

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Consider the voting system [7:A=3,B=3,C=2,D=2,E=2]. If A opposes a motion, but B, C, D, and E support it, does the motion pass? Which voters are critical? |

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Consider the voting system [7:A=4,B=3,C=3]. Construct a table of all possible elections and for each election identify which voters are critical. |

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The United Nations security council has 15 voting members, and a motion requires the support of 9 members to pass. However, 5 of the voting members have veto power. Construct a weighted voting system that would model the United Nations security council. |

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