You done maths wrong. The room is $30. They pay $10 each. They then are given $1 each. So they Pay $9 each, which is $2 extra, than the $25.
What you are saying, is that the men are only paying $9, when, in fact, they are actually paying $9.66, because of the $2 the bellboy is taking. There is no missing dollar. The cost of the room ($25) plus the cost of the bus boy($2) is equal to the amount paid by the 3 guests($27). They have the money given back to them($3, $1 for each) with themselves, which equals the total starting price of $30.
