1. Shopkeeper's discount price (25)+ waiter's hidden money (2)= passenger's current total cost (27)

2. The original cost of the passenger (30)= discounted fare (25)+ refund of the owner (5)

3. The original fare of the passenger (30)= the total fare of the passenger now (27)+ the refund fee finally received by the passenger (3).

4. Refund received by passengers (3)+ money hidden by the waiter (2)= refund from the owner (5)

5. That is to say, the amount spent by the three passengers in the end includes the part concealed by the waiter, so if you want to get the total amount, you should add the refund that the passengers finally received from 3 yuan, not the money concealed by the waiter.

This is just a trap of logical deviation.