Can You Figure This Out!?

Three guys all show up at a hotel at the same time. They all want a room.
The guy at the desk says "Sorry, there's a convention in town and all I got is one room."
After some negotiating, the three guys decide to split the cost of the one room.
The desk clerk says "That'll be $30." Each of the three guys pulls out a ten dollar bill and hands it to the guy at the desk.

After the guys go to the room, the desk clerk starts to feel guilty. You see, the room actually costed $25 bucks. So he calls the bell hop over and says "Here's five one dollar bills, take them to the guys in room 418."

The bell hop arrives at the room, explains the mistake with the cost of the room and hands them the five dollars. The guy that answers the door keeps a dollar, hands a dollar to each of the other two guys, and gives the bell hop a two dollar tip.

OK, here's what you have to figure out:

So each guy paid ten bucks, but got a dollar back . . . right?

Three times nine is $27, right?
The bell hop got a 2 dollar tip, right?
27 plus 2 is 29, right?
But they paid $30, didn't they?

Where's the other dollar?

Answer: 

You don't add your accounts payable against your accounts receivable. . . you subtract them.
They each paid 10, got a dollar back, 3 X 9 IS $27, then you SUBTRACT the two dollars to the bellboy, $25 the price of the Room