Question: Three guests check into a hotel room. The clerk says the bill is $30, so each guest pays $10. Later the clerk realizes the bill should only be $25. To rectify this, he gives the bellhop $5 to return to the guests. On the way to the room, the bellhop realizes that he cannot divide the money equally. As the guests didn't know the total of the revised bill, the bellhop decides to just give each guest $1 and keep $2 for himself. Each guest got $1 back: so now each guest only paid $9; bringing the total paid to $27. The bellhop has $2. And $27 + $2 = $29 so, if the guests originally handed over $30, what happened to the remaining $1?
Hint: Make a list of all of the people involved and how much money they ended up with/spent.
Answer: The $9 paid by each guest accounts for the $2 that went to the bellhop. So rather than adding $27 to the $2 kept by the bellhop, the $27 accounts for the bellhops money. The $27 plus the $3 kept by the guests does add up to $30.
By Martin Gardner
Question: You are in a room with two metal rods and no other metal. One of them is magnetized and the other is not.
How can you determine which one is magnetized and which is not?
Answer: Solution 1: Touch the end of one bar (A) to the middle of the other bar (B) forming a 'T' shape. If the bars are attracted then bar A is magnetized and if they are not attracted then bar B is the magnet. This is because magnets have fields at the poles (the ends) but not in the middle. So the end would attract and middle would not.
Solution 2: Hang a rod from the ceiling and if it turns north than it is the magnetized rod.