MISSING DOLLAR RIDDLE

Esta es muy buena. La respuesta va venir en el título.
Se las pongo en inglés, sorry x no traducir pero ando corto de tiempo y no quería dejar tanto tiempo sin postear.

Si alguien se la sabe ponga la respuesta en los comentarios. (no sean tramposos y la lean primero, confío en ustedes!)

Three guests check into a hotel room. The clerk says the bill is $30, so each guest pays $10. Later the clerk realizes the bill should only be $25. To rectify this, he gives the bellhop $5 to return to the guests. On the way to the room, the bellhop realizes that he cannot divide the money equally. As the guests didn’t know the total of the revised bill, the bellhop decides to just give each guest $1 and keep $2 for himself.

Now that each of the guests have been given $1 back, each has paid $9, bringing the total paid to $27. The bellhop has $2. If the guests originally handed over $30, what happened to the remaining $1?