You are standing in a pitch-dark room. A friend walks up and hands you a normal deck of 52 cards. He tells you that 13 of the 52 cards are face-up, the rest are face-down. These face-up cards are randomly distributed throughout the deck.
Your task is to split up the deck into two piles, using all the cards, such that each pile has the same number of face-up cards. The room is pitch-dark, so you can’t see the deck as you do this.
How can you do this seemingly impossible task?
Solution 1: 13 Cards cannot be distributed in 2 piles equally so the question is wrong.
try again
Split vertically in between the deck (tear off). So bingo.
Spoiler Alert!
Divide the pile into two stacks of 39 and 13. Then flip all cards (13) of second stack. Viola!
What if, in the 13 cards pile, one of the cards is already faced up? You just flipped down one card, and flipped up twelve. Like the questions says, the faced up cards are “randomly distributed.” How would you know?
Ah, I get it. Both piles would then have 12 faced up cards since one was removed and flipped faced down from the original deck. “same number of face up cards.”
DOH!
hahahahahaha….
I should have mentioned that those who know the answer should not post until midnight
you’re absolutely right Jareer
@Jareer, why don’t you try this one……
http://ranahammad.wordpress.com/riddles/two-ropes-burning/
Once a nice person asked me this question in an interview.
If anyone likes the solution, please do comment or share other solution or riddles. Thanking everyone
I do not understand how that is the right answer! I’m so confused. For my Calculus class my teacher gave me a question similar to this for extra credit…”There are 52 cards in a standard deck. Suppose you are blindfolded and someone gives you a standard deck in which 13 of the cards are facing up and the rest facing down. Make two stacks of cards such that both stacks have the same number of cards facing up.”
Is the answer still that you just have to divide the cards into two stacks of 39 and 13 and flip all of the 13 card pile over? So, are none of the cards facing up anymore?
Rana. What is the solution?
nice one