Each friend spent $9 on the room.
3 x 9 = 27
There's $2 in the bellhops pocket:
27+2 = 29
But wait..they started with $30!!! Where's the missing dollar gone?
I realize that "trick" questions are the point of brain teasers, but isn't it cheating to give false
information for your brain teaser?
The $27 they spent on the room includes the $2 in the bellhop's pocket. If you then say there are $2 in the bellhop's pocket and bump the number to $29 you're saying there are $4 in the bellhop's pocket. I'm wondering if that's intended as misleading information (say, including $2 in the bellhop's pocket that aren't related to this particular transaction), or if it's outright misinformation (given that the $2 in his pocket are actually included in the initial $27, meaning you can't add it twice to get $29).
See, the way you have it written there, they spent $29 on the room & bellhop and
got $3 back, which means there isn't one missing dollar, there are two extra
dollars (as you'd end up with $27 for room, $2 for bellhop, and $3 back to the friends - $32 total). That's if it's misinformation, as opposed to intentionally misleading via including two unrelated dollars.