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# Section 3.2 - PowerPoint PPT Presentation

Section 3.2. Two players: The Divider-Chooser Method. The best known of all continuous fair-division methods Can be used anytime there is a continuous fair-division problem. Division. Player 1: (The Divider) – divides the cake into two pieces that he feels are fair shares

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### Section 3.2

Two players:The Divider-Chooser Method

• Player 1: (The Divider) – divides the cake into two pieces that he feels are fair shares

• Player 2: (The Chooser) – picks the piece he wants, leaving the other piece to the divider

• When played properly, this method guarantees that both players get a share they believe to be fair

• Jake: Mom it’s the last slice [of bread].Mom: Hmm…Well then let’s share. We’ll cut it in half.Cody: His half can’t be bigger than mine!Mom: All right. I’ll tell you what. Jake gets to cut.Jake: Yes! [cuts a big piece for himself]Mom: But…Cody gets to choose.Jake: [sad about this new information, passes the plate]Cody: Nice…[after a moment, takes bigger piece for himself]. I got a pretty big half!Jake: [smiles despite ending up with a smaller piece]

• It is better to be the chooser because the divider always gets a piece that is worth exactly one-half, but the chooser may get a piece worth more than one-half

• A clever way to extend some of the ideas in the divider-chooser method to the case among three or more players

• For three players- 1 player is randomly chosen to be the divider and the other two players are to be the choosers C1 and C2

• Step 1: The Divider cuts the cake into 3 pieces, called S1, S2 and S3. The divider must cut the pieces into what he considers 1/3 of the value of the cake.

• Step 2: The choosers must declare their bids- they write on a slip of paper which piece or pieces they consider to be a fair share. They can vote on all three, but has to be at least one.

• Step 3: We distribute the pieces depending on the bids. There are 2 cases:

• Case 1: If C1 and C2 bid on different pieces, then C1 gets a piece, C2 gets a piece and the divider gets the piece that is not taken

• Case 2: If C1 and C2 bid on the same piece, they choose one of the other pieces to give to the divider. They then combine the other two pieces and use the divider-chooser method.

Page 117 # 15 There are 2 cases:

• What should the division be?

• A) Chase: Chandra: Divine:

• B) Chase: Chandra: Divine:

• C) Chase: Chandra: Divine:

• D) Chase: Chandra: Divine:

Page 117 # 15 There are 2 cases:

• What should the division be?

• A) Chase: S2 Chandra: S1 Divine:S3

• B) Chase:S2 Chandra:S1 Divine:S3

• C) Chase:S1 Chandra: S2 Divine:S3

• D) Chase: ½ (S1 + S2)

Chandra: ½ (S1 + S2) Divine: S3

For more than three players (N) There are 2 cases:

• Step 1: The divider cuts the cake into N pieces, all of which he considers to be a fair share

• Step 2: Each chooser makes their bid

• Step 3: Distribute the pieces

• Case 1: If every chooser has a different bid, the pieces are given to each chooser and the divider gets the last piece.

Assignment piece, then there is a

• Section 3.2: page 115 - 116 # 9, 10, 13, 14

• Section 3.3: page 117 – 119 # 16 - 24