A fifth puzzle from the set!
\begin{align}3+4&=17\\2+5&=7\\3+1&=2\\2+1&=1\\4+2&=0\\3+6&=\,\,?\end{align}
Can you find the value of the question mark?
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1$\begingroup$ The odd one out appears to be $2+5=7$ because that is the only correct equation, but that's all I can gather at this point in time. (I need to go to bed.) $\;$ Edit: Stuff it — I am working on this ;) $\endgroup$ – Mr Pie Jul 16 '18 at 15:02
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$\begingroup$ Am I just being unnecessarily pedantic or are others as uncomfortable as I am with this type of fake equation syntax? The real question here is not "what is the value of the question mark" but "What functional definition of '+' makes these equations work?" In which case, why not just write "Find a function f such that f(3,4)=17 etc"? $\endgroup$ – MattClarke Jul 18 '18 at 6:18
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1$\begingroup$ @MattClarke because not everyone enjoys math; sometimes, people need things to be nice and simple ;) $\endgroup$ – Mr Pie Jul 19 '18 at 1:40
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It's quite a bit higher than the rest, but I want to say the answer is
513
The formula being
AB - BA
All equations:
34 - 43 = 81 - 64 = 17 25 - 52 = 32 - 25 = 7 31 - 13 = 3 - 1 = 2 21 - 12 = 2 - 1 = 1 42 - 24 = 16 - 16 = 0 36 - 63 = 729 - 216 = 513
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1$\begingroup$ (+1) Correct. I'll have to make the next one trickier as everyone here is so smart :) $\endgroup$ – TheSimpliFire Jul 16 '18 at 15:57
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Here is a quick observation I made.
$$a+b:= \frac{a(a^2+b-1)}{2}-1$$
However,
This only works for the first two equations: $(a,b)=(3,4)$ and $(a,b)=(2,5)$
And
A quick glance at the answer above reveals that I am most likely not on the right track anyway...
