It's
A Trick on Words
It leads you to believe the answer is
30 and has you add the number 2 when you should be
subtracting as follows:
3 x $9 = 27 then minus the $2 = $25 which is what they paid
for the room.
And if you take what they ultimately paid for the room ($25)
and add the $3 ($1 each they received), and then add the $2 the
bellhop took, you would reach the original $30 that was paid.
