Three men walk into a hotel and ask for a room. The hotel clerk tells them it will be $30 for the night. Each men reach into their wallet and pull out a $10 bill. They paid $10 each for the room, totaling $30. But later, the clerk realizes he made a mistake, the bill was supposed to only be $25. He gives the bellhop $5 and tells him to return it to the men. On the way up to their room, the bellhop begins to contemplate how he can divide $5 between 3 people, being he is a Liberal, he decided the best thing to do would be, give each man $1 each ($3) and he would keep the other $2. So that is what he did. Now, this means, since each man originally paid $10 and each man got $1 back, they paid $9 each for the room. But... $9x3 =$27 Plus the $2 the bellhop kept, makes $29... where is the other dollar???
This is a hoary old chestnut.
[h=2]Solution[/h] The initial payment of $30 is accounted for as the clerk takes $25, the bellhop takes $2, and the guests get a $3 refund. It adds up. After the refund has been applied, we only have to account for a payment of $27. Again, the clerk keeps $25 and the bellhop gets $2. This also adds up.
There is no reason to add the $2 and $27 – the $2 is contained within the $27 already. Thus the addition is meaningless. Instead the $2 should be subtracted from the $27 to get the revised bill of $25.
This becomes clearer when the initial and net payments are written as simple equations. The first equation shows what happened to the initial payment of $30:
$30 (initial payment) = $25 (to clerk) + $2 (to bellhop) + $3 (refund) The second equation shows the net payment after the refund is applied (subtracted from both sides):
$27 (net payment) = $25 (to clerk) + $2 (to bellhop) Both equations make sense, with equal totals on either side of the equal sign. The correct way to get the bellhop's $2 and the guests $27 on the same side of the equal sign ("The bellhop has $2, and the guests paid $27, how does that add up?") is to subtract, not add:
$27 (final payment) - $2 (to bellhop) = $25 (to clerk) This is clearly not a
paradox, and involves only the switching of subtraction for addition. Each patron has paid $9 for a total of $27. The storyteller adds the $2 that the bellhop pilfered, but he should have subtracted the $2 to make a total of $25 paid. So 3 X $9 = $27, which accounts for the $25 room and the $2 theft.
http://en.wikipedia.org/wiki/Missing_dollar_riddle