Three people check into a hotel room and each of them gets charged $10 - a total of $30. Later the clerk realizes that the bill is just $25, so he sends the bellboy to return $5 to the guests. On his way to the room, the bellboy decides to cheat and pockets $2 of the money, and gives the three men just one dollar each. Now the three men have spent $9 each, for a total of $27. Additionally, the bellboy took $2 for himself, which adds up to $27 + $2 = $29. Since the guests originally handed over $30, the question is what happened to the remaining $1?
The calculation is made the wrong way. The three men originally gave $30, but later $5 of them were sent back, which makes it $30 - 5 = $25 left at the clerk. Each of them men spent $9, so they gave $27 in total, $2 of which ended up in the bellboy's pocket. $27 - $2 = $25, so no "missing dollar" here.
3 x $9 - $2 = $30 - $5.