[wenc]

I think most of us are impressed by computational parlor tricks (and indeed raw computational intelligence in general -- being able to process information and compute quickly and accurately), but for me, genius goes beyond that.

Genius is about having rare and useful insights that the rest of us are incapable of, and that a computer is unable to easily replicate.

For instance, there was this thing on Twitter recently about all percentages being reversible (7% of 50 is equal to 50% of 7, but the latter is easier to mentally calculate). Most of us are aware that multiplication is commutative, but it takes genius to recognize and frame that insight in a useful way.

[hnews_account_1]

I'm not that sure about computational intelligence being all that impressive. For instance, that parlour trick you mentioned is common enough to come across (I'm not particularly a super genius but I had it figured out by the time I was in college) that I was surprised that so many people found it useful. Like legit intelligent people were talking about how useful it was on Twitter. Which made me realise that some of us were just quicker with math even if our overall intelligence wasn't spectacular.

[psoy]

That's not an example of genius by any stretch of imagination, sorry.

[cheerlessbog]

It never occurred to me that 7% of 50 is equal to 50% of 7 perhaps because they are equally easy to calculate? Multiply 7 by 5 and fix the decimal point.

[wenc]

What about 17% of 50? 17*5 isn’t so simple anymore, whereas 50% of 17 is 8.5.

To be fair, with most shortcuts, it’s possible to construct difficult cases (17% of 23 is difficult in either order) but where it applies (when one of the pairs is a common percentage), exploiting commutativity can be quite useful. Plus the mental overhead of remembering the rule is extremely minimal.

[JadeNB]

How can you discover that 50% of 17 is 8.5 if you can’t multiply 17*5? (If the answer is “by halving”, then my response is that halving and then multiplying by 10 is often the easiest way to multiply by 5!)

[Sharlin]

I’m not sure, but to me at least halving 17 to get 8.5 is an almost completely intuitive process, whereas multiplying 17 by 5 seems to require an extra cognitive step to reduce it to shifting the decimal point and then halving (or vice versa). Never mind the extra step when presented by the problem of taking 17% of 50.