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From Russia with love (Posted on 2012-08-11) Difficulty: 4 of 5
Let n be a fixed integer.
Kostya has a black box, such that if you put in exactly 2n+1 coins of distinct weights, the box will expose the coin of median weight.
The teacher gave Kostya 4n+1 coins of distinct weights and told him which coin has the median weight.

Can Kostya check whether the teacher is right, using the box not more than n+2 times?

Source : Russian Euler contest 2012

Rem: Note that Kostya can't just put 4n+1 coins in the box.
The box accepts exactly 2n+1 coins.
Hint: start with n = 1. .

No Solution Yet Submitted by Ady TZIDON    
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re: Revised Solution (spoiler) Comment 3 of 3 |
(In reply to Revised Solution (spoiler) by Steve Herman)

S.H, excellent explanation!!
  Posted by Ady TZIDON on 2012-08-12 10:30:30

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