Pop Quiz Hotshot: Can You Solve The Dark Room Coin Riddle?

Submitted by: fancylad 3 months ago in Quizzes Science


You heard the travelers’ tales, you followed the maps, and now, you’ve finally located the dungeon containing a stash of ancient coins. The good news: the wizard who owns the castle has generously agreed to let you have the coins. The bad news: he’s not quite as generous about letting you leave the dungeon ... unless you solve his puzzle. Can you solve it and get out alive? Lisa Winer shows how.
There are 9 comments:
Male 4,093
My solution had coin tossing in it. I figured that if a coin was tossed, it'd have a larger chance of landing gold side down because gold is denser than silver. Keep tossing coins, and you'd eventually get out. Not efficient, more of a brute force method.
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Male 5,670
I didn't get it, if i dont see a path to the solution early on these kinds of riddles, i rarely get the answer.
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Male 12,019
I stumbled across it somewhat accidentally.

My original thought was just to select 20 coins you knew were gold from memory and then turn them upside down since the piles could be uneven. (logically if you can remember that there were 20 silver coins total you can probably remember large sections that were gold).

Then I wondered what would happen if you got a silver coin by accident and turned it upside down making it gold. So I figured it out and realized that was actually the answer and it didn't matter how many silvers you got in your 20 since you were deducting them from both piles.

The riddle is somewhat silly though. Think of stacks of coins where one half is silver and one half is gold. Since they are stacked you can only see the tops of the coins on the top. The rest you would be judging based on the sides of the coin and every coin would have a side that is half silver and half gold. It would be virtually impossible to tell which silver halves were the top halves of coins and which were the bottom halves without a lot of time and a carful examination. 
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Male 7,244
Elegant solution. Alas, I failed to figure it out on my own.
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Female 5,406
9
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3,166
melcervini I think you had it right with 42.
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Female 5,406
melcervini no... 1... no wait... 9
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Male 12,019
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