Let me try this:

There's no missing dollar because 30 minus 5 equals 25 plus the bell hop's 2 equals 27. Each of the guys ended up paying 9a pieceand 3 times 9 equals 27. At the end of the equation, you have to figure on 27 dollars as the total number spent, not 30 because30 is the old figure and will throw off the math.

Even then, it is still a little confusing to think about because the mind naturally gets tricked into referring back to the original 30.

Do I have it right or am I completely off?