i've noticed that some of you keep checking back on the riddle, probably looking for the answer. so here it is. (read the riddle first if you don't want it spoiled)

the problem is not in the math but in the suggested solution. it's the old misdirection trick. the riddle asks us why the $27 the guests paid plus the $2 the bellhop kept doesn't add up to $30.

but the $2 the bellhop kept was part of the $27 the guests paid! look at it from their perspective:

- they paid $30.
- they got back $3, leaving $27.
- of the $27, $25 went to the hotel and $2 went to the bellhop.

so the math is actually: $27 + $3 = $30 or the money they ended up paying plus the money they got back equals the money they originally paid.

if you still don't understand it completely, try cutting up 30 pieces of paper and following each bill separately.