Let me tell you something. Xtcgruc is right, "You confuse the concepts of absolute advantage and comparative advantage". You set an hour. In the comparative advantage, the time to produce two products is not equal, because the production efficiency is not equal. Equivalent to what? This is unit production. It is to produce a unit to weed, or to produce a unit to work (playing ball as a job). Tom needs 1 hour to produce a unit of weeding (we assume it is 100 yuan for weeding), and 1 hour for working to make money is his opportunity cost, which is a big number; On the other hand, it takes Tom very little time to produce a unit job (also assumed to be 100 yuan), because he plays ball with high efficiency to make money, and the income from weeding during this period is very small, so the opportunity cost is very small.

Then you will know what opportunity cost is. The unit quantity of B can be exchanged for the unit quantity of A, and the two opportunity costs are reciprocal.

In fact, you don't have to worry too much about this matter. It makes sense to understand with the absolute advantage of being easy to understand. Anyway, the purpose is to use efficiency and maximize benefits. All roads lead to the same goal.

In addition, the opportunity cost of a can be expressed as (efficiency B/ efficiency A)* unit quantity, and the general unit quantity can be 1, such as 1 yuan, 1 ounce. So the main influencing factor of opportunity cost is efficiency B/ efficiency A, which you can understand as the relative efficiency of B to A. In the case of playing ball, the relative efficiency is very low, so the opportunity cost is very low, which can be understood more directly.

Think about it more. It's still quite interesting.