The math is incorrect.
If they had been charged $27.00 for the room originally, they would have
each given the man $10.00, and each received $1 change, making the math
problem 9+9+9=27, and 27+3=30, the $3 being the key. Instead, the way
the problem reads, it is turned into 27+2=29, which is where the
confusion lies. The problem should be $25 (room rate) + $2 (what the
bellboy kept) = $27, and $27 + $3 (the change the three guys received) =