Speedometer Pinion Gear

Three people go to share a hotel room. They pay $30. After they get settled in, the manager realizes that he overcharged them by $5. So he sends the bellboy up with $5. He decides to give them a dollar each because he didn't have change. That means they paid $9 each for the room. $3 X $9 = $27. $27 + the $2 the bellboy kept = $29. Where's the other dollar?