When You Know It, You Know It

Three guys go in to a hotel, each with $10 in his pocket. They book one room at $30 a night. A short while later, a fax from headquarters directs the hotel to charge $25 a night. So the receptionist gives the bellhop $5 to take to the three guys sharing a room. Since the bellhop never got a tip from them, and because he can’t split the $5 three ways, he decides to pocket $2 and give them each $1 back. So each of the guys now has spent $9, and the bellhop has $2, for a total of $29. Where’s the extra dollar?