You walk into a dark room in which 100 coins are scattered around on the floor. 10 of them are heads up, 90 are tails up.
You cannot feel, see or in any other way find out on which side the coins are. How can you split the coins into two piles such that there are the same number of heads in each pile?
Riddle AnswerThere are 21 barrels of wine with a farmer. 7 are full, 7 are half full and 7 are empty. He wishes to divide them among his three sons such that each son has the same number of full barrels, the same number of half full barrels, and the same number of empty barrels. Note that there are no measuring devices handy. How can the barrels and wine be evenly divided?
Riddle AnswerYou have three boxes. One has only red marbles, one has only blue marbles and the third has an equal number of red and blue marbles. The labels on the boxes have intentionally been switched so that each box is now marked incorrectly.
Your job is to relabel the boxes correctly. Of course you could just look in the boxes to find out which labels match, but can you do it without looking into each box? Reach into any one of the boxes and select one marble. Can you now correctly label all three boxes? If not, select a second marble from any box. What is the fewest number of marbles you need to inspect in order to correctly label each box?
Riddle AnswerIf I had one more sister I would have twice as many sisters as brothers. If I had one more brother I would have the same number of each. How many brothers and sisters do I have?
Riddle Answer