Where is the missing $?

3 guys on a trip pull in to a hotel for the night. The owner usually charges $25 a night but is desparate for money so he charges the men $30. They pay $10 each and go to thier room. Later the owner feels quilty for over charging and tells his son to take the $5 and give it to the men. On his way the boy thinks to hisself that he cant divide the $5 between 3 guys so he put $2 in his pocket and gave the guys the other $3. So now each guy has paid $9 each which is $27 between the three of them. Add the $2 the boy kept and that $29. Wheres the other $1?