I think I have seen a nice riddle that you may like.

(This riddle has been translated so I hope that no valuable information has been lost):

Two friends walk in distant lands when they are trapped by the men of an evil king. They are imprisoned in different rooms without having time to talk to each other.

Both have a window in their room from which they see a garden.

One of them (Rick) can see 16 apple trees.

The other (James) can see 8 apple trees.

It is indicated that in the garden there are 24 or 26 apple trees, that none of the apple trees has been seen by both at the same time, and that between the two they can see all the apple trees in the garden.

During the following hours, the king will ask the same question. First, ask Rick: Are there 24 or 26 apple trees in the garden? "If he does not answer, he will ask James the same question.

If one of the two friends responds correctly, both will be released.

If one of the two responds incorrectly, both will be executed.

If they do not answer, the king will ask the other friend, a round consists of: "Ask Rick - ask James", always starting with Rick.

How many rounds are necessary to answer correctly?

Good luck

  • $\begingroup$ I'm pretty sure this is a duplicate of another question. Don't have a source though. $\endgroup$
    – AHKieran
    Mar 7, 2019 at 9:17
  • $\begingroup$ Hey, welcome! Would you mind adding the source for where this is from? Thanks! $\endgroup$
    – Mithical
    Mar 7, 2019 at 9:52
  • 1
    $\begingroup$ Very similar to this: puzzling.stackexchange.com/questions/73462/… which was also marked as a duplicate. $\endgroup$
    – hexomino
    Mar 7, 2019 at 9:53

1 Answer 1


my take is that the two people will get off on the

8th round, answered by James

Approaching this puzzle from the perspective of James,

Since James can see 8 trees, he knows that Rick has seen either a) 16 b) 18 trees

Breaking down the scenarios:
a) If Rick sees 16, he will think that James has seen 8/10 trees
b) IIf Rick sees 16, he will think that James has seen 6/8 trees
Using modified logic from the Blue Eye Oracle Problem, each round symbolizes one tree that James has seen.

On the 8th round, if Rick is scenario (b) and sees that James does not answer, he will know that James has at least 7 trees, leaving 18 + 8 = 26 trees as the answer.
However, Rick is (a) and knows that James has seen at least 8 trees, hence does not answer.

It should be evident to James that Rick has seen 16 trees.
Therefore he answers 16(a) + 8 = 24 on his turn during the 8th round.


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