Quarters Riddle
Posted by Rob Herman at October 26th, 2006
Solve this one yourself and be smarter than me. In retrospect it seems so obvious…
You are blindfolded and put in front of a table with 100 quarters. I tell you that 30 of the quarters show heads, and the rest show tails. How can you put the quarters into two piles such that the two piles have the same number of quarters showing heads?
No, you can’t use any other sense to determine what side of a quarter is which.
Hint 0: It only looks impossible.
Hint 1: Try it with a very small number of quarters, like 3.
I think this should be in the riddles section not the rpg section. Unless this part of some larger arc articles that will eventaully lead to “Quater Flipping: the RPG” where all your random numeric effects are generated by d2s plus some constant. Hit points and other resources are kept track of by various denominations of coins etc… I think that would be a stretch Rob, maybe you should just put this one in the riddles section.
Fixed. :P
Do we get an answer to this one?
Sure.
Take 30 quarters (any ones will do) out of the first pile to form the second pile, and flip all of them.
For every quarter you move to the second pile and flip, either:
1. It was a tail, so it’s a head now, and it matches one of the heads in the first pile
2. It was a head, so it’s a tail now, and that’s one less head you have to match.
Notice that each quarter you move aside and flip takes care of exactly one of the heads, so you move and flip a number of quarters equal to the number of heads you started with.
Of all the riddles this one seems most like a ‘trick’. Most unsatisfactory.
Instead of missing a poorly stated pun, or not thinking of an ambiguous metaphore I lacked the ability to guess at various manipulations.
I could have taken the $25 gotten dinner, eatten it, and been left with two equal piles of quarters each with 0 heads…
Most Unsatisfactory. ;)