So, the farmers agree to pay $10 each. They pay and go to their room.
But then, the hotel owner realises that he has forgotten his super discount. The farmers only had to pay $25. So, he calls the bell-boy and tells him to give the farmers their $5 back.
But the bell-boy thinks: "You can't split 5 by 3 well. If I give them their $5, they'll probably have a fight." So he keeps $2 for himself and gives the other $3 to the farmers.
Now, the farmers each paid $9, that's $27 in total, and the bell boy kept $2. But together, that's $29!
What happened to the missing dollar?