A friend of mine posted a riddle on Facebook involving adding money and then subtracting money. It ended with a question asking where $1 went, but the trick was that there was no discrepancy, so the $1 didn't exist.
The question: Three guys walk into a hotel, and they're going to split the cost of a room. The room is $30. They each kick in $10 and head up to their room. The manager gets wind of it and tells the clerk the room is only $25. He hands five $1 bills to the bell hop and tells him to go refund the guys' money. On the way up to the room, the bell hop gets to thinking, as bell hops are wont to do, and says to himself, "No way can three guys split $5, I'm going to help out." He stuffs $2 in his pocket, knocks on the door, gives each guy back a buck and heads back downstairs to the desk, glowing in the warmth of a job well done. So now each guy has paid $9. $9 times 3 is $27 plus $2 the bell hop stole--only $29! Where is the other buck?
(I bolded the question)
I said the question was invalid, but my friend pointed out that every question is valid to ask.
What would I call this question that has no answer? (If I understand correctly rhetorical is when you can answer the question, but it is not meant to be answered, so by that definition "rhetorical" would be invalid here.)