One hundred people entered a hotel that had 99 rooms, and each of them asked for their own room. In order to solve the problem, the bellboy did the following:
He asked the 100th guest to wait for a while with the 1st guest in room number 1, so that there were 2 guests inside. Then he took the 3rd guest to room number 2, the 4th guest to room number 3, and so on, until finally taking the 99th guest to room number 98. At the end he returned to room number 1 and took the 100th guest to room number 99, which was still vacant.
How could everybody get their own room?
The two people who were taken to room number 1 were guest 1 and guest 100. Thus, the 2nd guest ended up without a room.