I'm trying to solve this puzzle. Numbers are at triangle, and I have to solve ?-mark:
5
6 1
7 2
5 ? 7 5
Based on solutions it should be ?=7. But I don't understand the reason for this
I also put pic of it.
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$\begingroup$ There could be dozens of answers with a reasonable logic. For instance, it should be 2 as in every little triangle there are two numbers whose sum is the third. $\endgroup$ – Arnaud Mortier Sep 15 at 6:50
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$\begingroup$ Can you then name one explanation, why the answer would be seven? $\endgroup$ – No name Sep 15 at 6:59
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1$\begingroup$ What is the source for this puzzle? A textbook, competition, ... ? $\endgroup$ – Rand al'Thor Sep 15 at 7:03
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$\begingroup$ Yes, for instance: every number should appear an odd number of times. $\endgroup$ – Arnaud Mortier Sep 15 at 7:07
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1$\begingroup$ Thanks Arnaud Mortier! Good explanation $\endgroup$ – No name Sep 15 at 7:10
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It is:
7. Start with $5,5,5$. The sum is $15$. Move each circle clockwise one step. You now have $1,7,7$, again the sum is $15$. Moving clockwise again you have $2,?,6$. For the sum to be $15$, $?=7$.
