If we assume that both countries specialize according to their comparative advantage, then how do we find a terms of trade that will cause both entities (i. e. individuals, countries) to be better off?

The best way to find terms of trade that will ensure that two entities are in the best terms of trade will be to look at the opportunity costs of the various products they produce.

A high opportunity cost in one product relative to that of the other entity means the entity with the higher opportunity cost should be trading with the entity with the lower opportunity cost and vice versa.

For example, assume that an entity "A" produces both rice and beans whilst an entity "B" also produces rice and beans too.

If the opportunity cost to A of producing Beans is 300 bags of rice whilst the opportunity cost to B of producing Beans is 120 bags of rice, and the opportunity cost to A of producing rice is 180 bags of beans whilst it is 250 bags of beans to B, the principles of comparative advantage require that A should focus more on producing rice and purchase beans from B whilst B should focus more on producing beans and purchase rice from A.

Cheers!

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