It’s been a little while.
A Bus has three stops on its route. A ticket costs 12 cents if you’re going to the first stop, 21 cents if you’re going to the second stop, and 25 cents if you are headed to the third stop. A man gets on the bus at the starting station, and hands the driver 25 cents. Without communicating with the passenger at all, the Bus Driver hands the passenger a ticket to the 3rd stop. How did he know?