Teresa and Beth are roommates. They spend most of their time studying (of course), but they leave some time for their favorite activities: making pizza and brewing root beer. Teresa takes 4 hours to brew a gallon of root beer and 2 hours to make a pizza. Beth takes 6 hours to brew a gallon of root beer and 4 hours to make a pizza.
Teresa's opportunity cost of making a pizza is (2/3 gallon, 5/7 gallon, 1 1/2 gallons, 1 2/5 gallons ) of root beer, and Beth's opportunity cost of making a pizza is (2/3 gallon, 5/7 gallon, 1 1/2 gallons, 1 2/5 gallons) of root beer.
(Teresa, Beth?) has an absolute advantage in making pizza, and (Teresa, Beth) has a comparative advantage in making pizza.
If Teresa and Beth trade foods with each other, (Teresa, Beth?) will trade away pizza in exchange for root beer.
The price of pizza can be expressed in terms of gallons of root beer. The highest price at which pizza can be traded that would make both roommates better off is (2/3 gallon, 5/7 gallon, 1 1/2 gallons, 1 2/5 gallons) of root beer, and the lowest price that makes both roommates better off is (2/3 gallon, 5/7 gallon, 1 1/2 gallons, 1 2/5 gallons???) of root beer per pizza.