Skip to main content
\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)
Mathematics LibreTexts

18.3: Weighted Voting

  • Page ID
    34291
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)

    1.

    1. 9 players
    2. \(10+9+9+5+4+4+3+2+2 = 48\)
    3. 47

    3.

    1. 9, a majority of votes
    2. 17, the total number of votes
    3. 12, which is 2/3 of 17, rounded up

    5.

    1. P1 is a dictator (can reach quota by themselves)
    2. P1, since dictators also have veto power
    3. P2, P3, P4

    7.

    1. none
    2. P1
    3. none

    9.

    1. 11+7+2 = 20
    2. P1 and P2 are critical

    11. Winning coalitions, with critical players underlined:

    \(\left\{\underline{\mathrm{P} 1}, \underline{\mathrm{P} 2}\right\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3\}\{\underline{\mathrm{P} 1, \mathrm{P} 2}, \mathrm{P} 4\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3, \mathrm{P} 4\}\{\underline{\mathrm{P} 1, \mathrm{P} 3}\}\{\underline{\mathrm{P} 1, \mathrm{P} 3}, \mathrm{P} 4\}\)

    P1: 6 times, P2: 2 times, P3: 2 times, P4: 0 times. Total: 10 times

    Power: \(\mathrm{P} 1: 6 / 10=60 \%, \mathrm{P} 2: 2 / 10=20 \%, \mathrm{P} 3: 2 / 10=20 \%, \mathrm{P} 4: 0 / 10=0 \%\)

    13.

    1. \(\{\underline{\mathrm{P} 1}\}\{\mathrm{P} 1, \mathrm{P} 2\}\{\underline{\mathrm{P} 1}, \mathrm{P} 3\}\{\underline{\mathrm{P} 1}, \mathrm{P} 4\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 4\}\{\underline{\mathrm{P} 1}, \mathrm{P} 3, \mathrm{P} 4\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3, \mathrm{P} 4\}\) P1: 100%, P2: 0%, P3: 0%, P4: 0%
    2. \(\{\underline{\mathrm{P} 1, \mathrm{P} 2}\}\{\underline{\mathrm{P} 1, \mathrm{P} 3}\}\{\underline{\mathrm{P} 1, \mathrm{P} 4}\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 4\}\{\underline{\mathrm{P} 1}, \mathrm{P} 3, \mathrm{P} 4\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3, \mathrm{P} 4\}\) P1: 7/10 = 70%, P2: 1/10 = 10%, P3: 1/10 = 10%, P4: 1/10 = 10%
    3. \(\{\underline{\mathrm{P} 1, \mathrm{P} 2}\}\{\underline{\mathrm{P} 1, \mathrm{P} 3}\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3\}\{\underline{\mathrm{P} 1, \mathrm{P} 2}, \mathrm{P} 4\}\{\underline{\mathrm{P} 1, \mathrm{P} 3}, \mathrm{P} 4\}\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3, \mathrm{P} 4\}\) P1: 6/10 = 60%, P2: 2/10 = 20%, P3: 2/10 = 20%, P4: 0/10 = 0%

    15. \(\mathrm{P} 3=5 . \mathrm{P} 3+\mathrm{P} 2=14 . \mathrm{P} 3+\mathrm{P} 2+\mathrm{P} 1=27,\) reaching quota. \(\mathrm{P} 1\) is critical.

    17. Sequential coalitions with pivotal player underlined

    \(<\mathrm{P} 1, \underline{\mathrm{P} 2}, \mathrm{P} 3><\mathrm{P} 1, \underline{\mathrm{P} 3}, \mathrm{P} 2><\mathrm{P} 2, \underline{\mathrm{P} 1}, \mathrm{P} 3><\mathrm{P} 2, \underline{\mathrm{P} 3}, \mathrm{P} 1><\mathrm{P} 3, \underline{\mathrm{P} 1}, \mathrm{P} 2><\mathrm{P} 3, \underline{\mathrm{P} 2}, \mathrm{P} 1>\)

    \(\mathrm{P} 1: 2 / 6=33.3 \%, \mathrm{P} 2: 2 / 6=33.3 \%, \mathrm{P} 3: 2 / 6=33.3 \%\)

    19.

    1. 6, 7
    2. 8, given P1 veto power
    3. 9, given P1 and P2 veto power

    21. If adding a player to a coalition could cause it to reach quota, that player would also be critical in that coalition, which means they are not a dummy. So a dummy cannot be pivotal.

    23. We know P2+P3 can’t reach quota, or else P1 wouldn’t have veto power.

    P1 can’t reach quota alone.

    P1+P2 and P1+P3 must reach quota or else P2/P3 would be dummy.

    1. \(\left\{\underline{\mathrm{P} 1}, \underline{\mathrm{P} 2}\right\}\left\{\mathrm{P} 1, \underline{\mathrm{P} 3}\right\}\left\{\underline{\mathrm{P} 1}, \mathrm{P} 2, \mathrm{P} 3\right\}\). P1: 3/5, P2: 1/5, P3: 1/5
    2. \(<\mathrm{P} 1, \underline{\mathrm{P} 2}, \mathrm{P} 3><\mathrm{P} 1, \underline{\mathrm{P} 3}, \mathrm{P} 2><\mathrm{P} 2, \underline{\mathrm{P} 1}, \mathrm{P} 3><\mathrm{P} 2, \mathrm{P} 3, \underline{\mathrm{P} 1}><\mathrm{P} 3, \underline{\mathrm{P} 1}, \mathrm{P} 2><\mathrm{P} 3, \mathrm{P} 2, \underline{\mathrm{P} 1}>\)

    \(\mathrm{P} 1: 4 / 6, \quad \mathrm{P} 2: 1 / 6, \quad \mathrm{P} 3: 1 / 6\)

    25. \([4: 2,1,1,1]\) is one of many possibilities

    27. \([56: 30,30,20,20,10]\)

    29. \([54: 10,10,10,10,10,1,1,1,1,1,1,1,1,1,1]\) is one of many possibilities


    18.3: Weighted Voting is shared under a CC BY-SA 3.0 license and was authored, remixed, and/or curated by David Lippman via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

    • Was this article helpful?