This question is an interview question for the company. The premise of consideration is to put the company's "interests" in the most important position, and the answer is -2 yuan, which means losing 2 yuan.

The correct answer is as follows: -2 yuan! 1. At first, there was only 9 yuan, and finally you had 12 yuan, so you earned 3 yuan; 2. The protagonist lost 9 pieces for the first time and got a chicken for the second time; The hero gains 10 and loses a chicken; On the third sale, the hero lost 1 1 and got a chicken; In the fourth transaction, the protagonist gets 12 and loses a chicken, so the GDP (gross domestic product) is 9+10+12 = 42 yuan +4 chickens. There are three transactions in the whole event. Let's see which three transactions are specific. The first transaction: 9 yuan buys, 10 yuan sells, and gains 1 yuan; The second transaction: 10 yuan sells, 1 1 yuan buys, and gains-1 yuan; The third transaction: 1 1 yuan to buy, 12 yuan selling profit 1 yuan; The whole process:1-1+1=1yuan, so the analysis shows that this person is a fool, because the last two transactions are equal to nothing. After testing, the enterprise believes that the answer to profit is 2 yuan's affirmation and interview failure; It is even more stupid to answer 3 yuan, because if you don't know what the additional cost is, you will definitely fail; If you answer 1 yuan, congratulations, it is not within the scope of fools; As a result, 3 yuan could have made a direct profit, but after three transactions, the total profit became 1 yuan. So the correct answer is: -2 yuan.