Three college students on a road trip decide to spend a Saturday night in a hotel. They go to check in and the night clerk tells them a room will be $30. They only have $10 each so they pay him the $30 and head up to the room.
The manager overheard the conversation and then explains to the night clerk that rooms are cheaper on weekends, so instructs him to go give them $5 back. The night clerk, on his way to the room, realizes he can't split $5 among three people so he pockets $2 and gives them back $1 each.
So if the students originally paid $10 each but got $1 back (3 X $9 = $27)... and the night clerk kept $2 ($27 + $2 = $29)...
Where did the other $1 go?