Missing dollar

3 guys want to share a hotel room and the costs. The clerk charges them $30 ($10 apiece) and sends them up to their room so they can rest. Later he discovers that he's overcharged them for the room, the correct rate for that room is only $25 per night. He sends the bell hop up to their room with their $5 refund. On the way up to their room the bell hop is wondering how he's supposed to split $5 between 3 different guys. In order to avoid the hassle he pockets $2 of the $5, leaving a $3 refund to split between the 3 friends. He does this and leaves... everyone is happy right? Except for the mathematician... the 3 friends each paid $9 apiece for the room ($10 minus the $1 refund) which makes a total cost of $27 ($9 times 3) for the room. $27 plus the $2 the bell hop kept only equals $29 where'd the missing dollar go? In the mathematicians wallet, that's his cut for making you believe that numbers are perfect...

I once knew the solution, but now I've forgotten...
Can someone help me?

All I do remember is that it's the wrong question that's asked.

That's not it...

30 - 3 = 27
the 2 left (from the five) are for the bell boy, and not the three left from above...

Another way of looking at it :

The facts in this riddle are clear: There is an initial $30 charge. It should have been $25, so $5 must be returned and accounted for. $3 is given to the 3 friends, $2 is kept by the bellhop - there you have the $5. The trick to this riddle is that the addition and subtraction are done at the wrong times to misdirect your thinking - and quite successfully for most. Each of the 3 friends did indeed pay $9, not $10, and as far as the friends are concerned, they paid $27 for the night. But we know that the clerk will tell us that they were charged only $25 and when you add the $3 returned with the $2 kept by the bellhop, you come up with $30.