Three people check into a hotel room that costs $30. They each contribute $10, handing $30 to the hotel clerk. Later, the clerk realises the room only costs $25. To rectify this, the clerk gives $5 to the bellboy and asks him to return it to the three guests.
The bellboy, however, decides to keep $2 for himself and gives $1 back to each of the three guests. Now, each guest has paid $9 (totaling $27) and the bellboy has $2, which makes $29.
Where is the missing Dollar?