The hotel accepts 30 yuan, gives preferential treatment to 5 yuan, and pays 25 yuan.
The waiter put 2 yuan's money in his pocket =27-25.
So there is no such thing as three people paying 9 yuan, 3*9=27 27 plus the 2 yuan money pocketed by the waiter 27+2=29.
Three people each pay 9 yuan, 3*9=27, the waiter pocketed 2 yuan's money, and the hotel took 25 yuan. 27-2=25"