How good is yer math?

3 hillbillies from gatlinburg Tennessee check into a hotel up north. The room is $30 a night. They all pay $10. The manager finds out they're hillbillies & decides to give them $5 back. The bellboy doesn't know how to give them good change. So he decides to give them $1 & take $2 for himself. Now the total is $9 each 3x9=27 the bellboy kept $2 1x2=2 so 27+2=29. What happened to the other dollar?