?3 guys check into a hotel. they are charged $30, so they pay...

?3 guys check into a hotel. they are charged $30, so they pay $10 each. the manager tells the porter he had overcharged the guests and it should have been $25. Go and refund them the difference. So the porter goes up and gives them $1 each and pockets the remaining $2. The guests paid $9 each ($10-$1) three x $9 is $27 and the porter pocketed the $2... that equals $29 where did the other $1 go?