Everyone actually paid 90 yuan money (100 first and 10 back), so three people actually paid 270 yuan. There's nothing wrong with that. The point is, please note that the 20 yuan money hidden by the waiter has been included in the 270 yuan. In other words, 270 yuan, including 250 yuan's accommodation, and 20 yuan were hidden by the waiter. Therefore, 270 yuan plus 20 yuan is a meaningless and unreasonable formula, which is purely misleading and leads to confusion.

Therefore, the relationship between 270 yuan and 20 yuan means that 20 yuan is included in the 270 yuan. It can be said that 270 yuan minus 20 yuan is the accommodation fee, but it cannot be said that 270 yuan plus 20 yuan. 20 yuan has been included in the 270 yuan. What else should we do? If you want to calculate the original 300 yuan, it should be 270 yuan (three people pay) plus 30 yuan (three people pay), which is the original 300 yuan.

1where is the problem of 0 yuan's disappearance?