There is no shortage of a dollar. Everyone only goes out of 9 yuan, and three people go to 27 yuan. The hotel charge is 25+2 (waiter hides) =27, and there is no shortage. Ten dollars per person, that is, thirty people's willingness to pay is 10 yuan; The boss is willing to sell 25 yuan; Party A, Party B and Party C actually pay 9 yuan each, and the consumption balance per person is 1 yuan ***3 yuan; The boss actually gets 27 yuan, that is, producer surplus 2 yuan.

Since the payment intentions of Party A, Party B and Party C are not clear in the title, we regard Party A, Party B and Party C as passive price recipients, from which the boss can get 2 yuan. Of course, from the arithmetic point of view, the result is that Party A, Party B and Party C each pay less 1 yuan, and the boss gets less 3 yuan.

Other common sense about mathematical thinking.

Mathematical thinking is what people usually call mathematical thinking ability, that is, the ability to think and solve problems from a mathematical perspective. For example, reduction, from general to special, from special to general, the idea of function/mapping and so on. Generally speaking, people with strong mathematical ability basically have two abilities, one is association, and the other is digital sensitivity.

The former can link two seemingly unrelated problems, among which structural ability is the most convincing; The latter is the most exposed so-called geek, such as Nash and so on. Of course, there are also two abilities combined.