At the beginning, each ABC spent 10 yuan, and ***30 yuan was in the hands of the vegetable vendor.
D bargain vegetable dealer returned to 5 yuan, leaving 25 yuan D to 27 yuan, 2 yuan.
Agricultural Bank of China gets back 1 yuan each time, which is equivalent to every consumption of 9 yuan ***27 yuan.
PS: 30-3 * 9 = 3, while D only took 2 yuan, leaving 1 yuan.
30-3*9=3 This 3 doesn't even include the 2 yuan money that D got.
This formula should be interpreted as abc's original value 30-abc's actual money 27=abc's money 3.
The actual money taken by ABC is 3= money taken by vegetable farmers+money taken by D is 2, of which the money taken by vegetable farmers = original 30- returned to 5 yuan.
That is, 27 = (30-5)+2. The wrong link should lie in the true meaning of the quantities on both sides of the equation.