Knights, Knaves, Jokers II

Logic Level 1

Suppose you are visiting an island with knights who always tell the truth, knaves who always lie, and jokers who can do either.

You meet three islanders named Ellis, Farin, and Gobi. They make the following statements:

If you know exactly one of them is a joker , how many of them are knights?

None of them are knights One of them is a knight Two of them are knights

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7 solutions

Ellis, Farin and Gobi all claim that the next person is a joker.

(Without loss of generality) let 's say that Elis is the joker . Now, trivially Gobi is correct and hence, he must be a knight because there is exactly one joker. This means that Farin is a Knave , since we have established that Gobi is a knight (and hence not a joker).

It is not necessary that Eli is the joker, however, regardless of whoever the joker is, we could repeat the above argument and show that there is exactly one knight. This nice property is because of the fact:

Elis claims joker Farins claims joker Gobs claims joker Elis \text{ Elis } \xrightarrow{\text{claims joker}} \text{ Farins } \xrightarrow{\text{claims joker}} \text{ Gobs } \xrightarrow{\text{claims joker}} \text{ Elis }

This is a great explanation

joshua ennis - 4 years, 4 months ago

Chioose Gobi as a jocker: Gobi is Jocker who Lies (this time) about Ellin who is knave and who lies about Farin who is knight who does not lie about gobi. Hence there is one knight: Farin. A similar result applies if Ellin or Farin is a jocker.

Raul Lopez - 2 years, 3 months ago
Oscar L
Jan 15, 2017

They all claim differently that a different person is joker, and all of them have claims against them about being a joker. Per the instructions, only one of them is a joker. Therefore, only one of them is right (the Knight)

Marcho Tridyo
Nov 4, 2017

A claims B is a joker, B claims C is a joker, and C claims a is a joker.

Suppose A is the real joker, so B and C aren't jokers. Hence, if B said that C is a joker he's lying, so he's a knave. And when C said that A is a joker that's the truth, so he's the knight.

This pattern repeats even if you suppose B is the joker (C is the knave, and A is the joker) and if you suppose C is the joker (A is the knave, and B is the knight)

And so, you'll always get the number of 1 joker, 1 knave, and 1 knight.

Saya Suka
Jan 11, 2017

Since only one is joker, the person who 'introduced' this joker cannot be another joker, so he must be a knight. And since there can be only one truth out of the three statements (only one joker), there is only one knight out of them.

Why can there be only one truth?

joshua ennis - 4 years, 4 months ago

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because we have been told there is just 1 joker.

Saya Suka - 4 years, 4 months ago
George Melas
Jan 20, 2017

Let Ellis be a joker then the other two are either knight or knave. Since Gobi says that Ellis is a joker then he is a knight. One knight is all we know.

Abhishek Medtiya
Jan 12, 2017

Suppose Ellis is a jocker and in first case he tells the truth so by his statement farin is a jocker but in given question only one person is knight so the farin is wrong and in the last statement which was told by gobi that ellis is a jocker so only one and only person who is a knight I think you got it.

Gary Jiang
Jan 21, 2017

If there's a joker,then there must be a knight. If there're two knights,then it's disobeying the facts. So X the number of knights/ 0<X<=1 /

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