Mathematical Riddle #1

3 alien check into a hotel in Kuala Lumpur. The receptionist tells them the room will be RM30. Each alien pays RM10 before going to the room. The clerk then realizes that they were given only a RM25 room, and sends the bellhop to the room with RM5. The bellhop keeps RM2 as tip and each man gets RM1 back, ending up paying only RM9 for the room. Three times RM9 is RM27. With the RM2 the bellhop kept, that's only RM29. Where's the missing dollar?

p/s : solution will be posted tomorrow.