3 friends go to a restaurant the bill is 30 dollars so they each pay 10 the waitress comes back and says she made a mistake it was only 25 so she gave 5 to the bus boy and said split it between 3 people he didn’t know how to do that so he kept 2 and gave us 3 back. Now that would make all of us pay 9 piece. 9 times 3 is only 27 the bill was 30 dollars and the bus boy kept 2. 27 plus 2 is only 29 what happened too our dollar