woohoo i figured it out. its a trick question. the cost payed by the guests was initially 30, right? there was no missing dollar. five dollars the bell boy had and the remaining 25 were with the proprietor. Yes, the guests payed 27 but they should have payed 25. this represented by the money that the bellboy pocketed. this money isn't added to the cost but represents the money that the guests SHOULD have recieved. thus the equation is 27-2 which is 25. so there is no missing dollar