Average revenue-average cost: (9+11)/2-(8+10)/2 =1.

Second, earn two dollars.

Sales-cost: (9+11)-(8+10) = 2.

Three, lose four dollars.

Maximizing economic benefits: 8 yuan can sell 1 1 yuan, and two transactions should have earned 6 yuan. As a result, I only earned 2 yuan, so I lost 4 yuan.

Summary:

1. The first algorithm is based on the premise that the market cost price of goods fluctuates. (More in line with practical thinking)

2. The second algorithm, provided that the market cost price of the commodity remains unchanged. (More like a pure mathematics problem)

2. The third algorithm is the pursuit of market economy. (idealized model)