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I've been struggling with this puzzle for the last few days.

We have square

$$\begin{bmatrix} 3 & 6 & 2 & 8 \\ 2 & 1 & 1 & 3 \\ 1 & 3 & 1 & 4 \\ 5 & 5 & 3 & ? \end{bmatrix}$$

Question is what number we should insert instead of question mark ?

Asaf Karagila
  • 393,674
Kevin
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  • The answer is $42$. I'm sure you will be able to find an argument for that (e.g. a polynomial of sufficient degree and some evaluations of it), as you would for almost all other solutions... Now the real question is: How do we know which system was in the mind of the one forming the puzzle, do we know his level of mathematical knowledge and thus the depth of the solution he had in mind? :) – Dirk Oct 20 '17 at 10:01