Gains from exchange: the two worth lines start far apart at 20 bottles each and converge as Joe sells to Sam
Sam — buyer, starts with 20 bottles
Joe — seller, starts with 20 bottles
0.2
0.4
0.6
0.8
1.0
1.2
Granola bars per bottle
16
20
24
28
32
8
12
16
20
24
Bottles Sam holds
Bottles Joe holds
Sam’s personal worth
of one more bottle
Joe’s personal worth
of one more bottle
Sam’s gain
Joe’s gain
No bottles traded yet
Sam: 1.00
Joe: 0.20
Both men still hold 20 bottles · no gains captured yet
Next bottle: worth 0.98 to Sam, only 0.22 to Joe — that gap is the reason to trade
Both start with the same 20 bottles — they just value them differently, so the two brass worth lines start far apart.
Drag either brass dot to move bottles from Joe to Sam and watch the lines close the gap (arrow keys work too).
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