You have fifty quarters on the table in front of you. You are blindfolded and cannot discern whether a coin is heads up or tails up by feeling it. You are told that x coins are heads up, where 0 < x < 50. You are asked to separate the coins into two piles in such a way that the number of heads up coins in both piles is the same at the end. You may flip any coin over as many times as you want.
How can you do it?
Take x coins, flip all of them and put them in one pile. The rest of the coins form the second pile.
4 Comments on "Fifty Quarters"
nicole says
December 29, 2014 @ 09:43
I don’t really get that joke but whatever…
Btw thanks for the people that offered to put the riddles on this website
Matthew says
July 22, 2016 @ 22:20
Presumably that only works if you know for certain that none of the x coins you are flipping are any of the original x coins already heads up, but how would you know that, if they are all mixed in front of you?
So you would need to be told not only how many are heads up, but which ones (or at least generally where in the group of coins) they are, so you can avoid them to begin flipping the same number of other coins.
Also presumably x must be no more than 25 so that you could flip the same number of coins which begin heads down.
In any case, this is a good-fun website, thanks.
Jake says
August 1, 2016 @ 04:37
Matthew, you’re wrong, it works no matter what. Even If you flip some or all the coins that are already heads up, it always works. Try it out yourself.
brainy spiegs says
November 11, 2016 @ 21:42
PLEASE FIX YOUR RIDDLE TO SAY THAT YOU CAN USE x IN YOUR ANSWER!!!!!!!!!!
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