This story takes us back to the times of King Vikramaditya. The king was possessed by a demon called Betal who once asked him a tricky question to judge his wit. He showed him three coins (gold, silver and copper) and told him that if he made a true statement, he'll get a coin else he won't be getting any of the coins. Imagine yourself to be Vikramaditya and try and make an apt statement which would ensure that you get a gold coin.
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3 Answers
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"You'll either give me the gold coin or no coin."
If the demon gives the gold coin, the statement was true and I received a coin, so everything is OK.
If the demon gives me a silver or copper coin, the statement was false and I received a coin, so it can't happen.
If the demon gives me no coin, the statement was true and I received no coin, so it can't happen.
As you see by asking "You'll either give me the gold coin or no coin." the only possible outcome would be receiving the gold coin.
EDIT for clarification:
Let's imagine the two scenarios, where the sentence I said is true and where it's false.
First Scenario ("You'll either give me the gold coin or no coin." is true):
Since it's true, the demon will give me a coin; but if it's true and the demon gives me a coin, it must be the gold coin (since it was true that he would give me the gold coin).
Second Scenario ("You'll either give me the gold coin or no coin." is false):
Since it's false, he will give me no coin. But we just assumed that the statement "You'll give me no coin" (a variant of it actually) is false.
Therefore, Second Scenario can't happen.
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$\begingroup$ Why the last two can't happen? And I didn't understand the copper and silver part. $\endgroup$ Commented May 7, 2015 at 10:17
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2$\begingroup$ @AdityaAgarwal The answer assumes that the demon is bound by the rules as given. So there is no finally involved, the demon would break the rules if he gives a silver coin and no gold coin. $\endgroup$– TaemyrCommented May 7, 2015 at 10:26
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1$\begingroup$ You could also say "You will not give me a copper coin or a silver coin." Logically, it is exactly the same, but some might find the explanation easier. $\endgroup$ Commented May 7, 2015 at 13:05
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3$\begingroup$ So what would the demon do if you said "You will give me no coins." ? $\endgroup$– David KCommented May 7, 2015 at 15:29
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2$\begingroup$ How about "If you give me any coins, you will give me the gold coin along with a chest full of rubies and a lifetime supply of Wonka bars." $\endgroup$– supercatCommented May 7, 2015 at 21:27
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Why stop at one coin? Get all three!
Just say:
The number of coins you give me can be divided by 3 without remainder!
This is exactly true when he gives you 0 or 3 coins. As a true statement together with 0 coins is not possible, the demon Betal has to give you all three coins, including the gold coin!
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$\begingroup$ Your answer assumes the fact that more than one coin can be given. You could take the statement
he made a true statement, he'll get a coin else he won'tliterally and say that you only get one coin. $\endgroup$– tfitzgerCommented May 8, 2015 at 15:12 -
$\begingroup$ @tfitzger if you take the statement literally it just means 'he gets a coin', not 'he gets only one coin'. And the statement 'he gets a coin' is true, regardless if he also gets another coin after that or if the Daemon also gives him a castle, it stays true as long as he did in fact get (at least) a coin. $\endgroup$– FalcoCommented Jul 6, 2021 at 13:19
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Why not use force?
"Either you will give me the gold coin OR I will commit suicide."
Explanation:
Since the demon is possessing you, it must comply, or perish alongside you.
