Solution for number 7

Well, this is mostly a problem dealing with common sense, and it is easy to get fouled up. The basic idea to its solution is that you should not be adding $27+$2 to get $30 ! The men are in debt, they have paid thirty dollars. Then they get five back, so that they have paid $25. When they tip the bagboy $2, they are then in debt $27, and the bagboy HAS two of those dollars. So, it is $27 - $2 = $25, which it should be. The hotel ends up with $25, the bagboy with $2, each man having paid $9, as they should have.