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Cognitive misers November 7, 2010

Posted by Ezra Resnick in Logic, Puzzles, Reason.
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Jack is looking at Anne, while Anne is looking at George. Jack is married, while George is not. Is there a married person looking at an unmarried person?

(a) Yes; (b) No; (c) It cannot be determined.

Make your choice before reading on.

According to psychologist Keith Stanovich (in an article by Kurt Kleiner), more than 80 percent of people answer this question incorrectly. It seems as though we need to know whether Anne is married; but a bit of further thought shows that it doesn’t matter. If she’s unmarried, then a married person (Jack) is looking at an unmarried person (Anne). And if she is married, then a married person (Anne) is looking at an unmarried person (George). So the answer is Yes in any case.

The solution is obvious once we think it through, so why did we get it wrong to begin with? According to Stanovich,

We are all “cognitive misers” who try to avoid thinking too much. This makes sense from an evolutionary point of view. Thinking is time-consuming, resource intensive and sometimes counterproductive. If the problem at hand is avoiding the charging sabre-toothed tiger, you don’t want to spend more than a split second deciding whether to jump into the river or climb a tree.

So we’ve developed a whole set of heuristics and biases to limit the amount of brainpower we bear on a problem. These techniques provide rough and ready answers that are right a lot of the time — but not always.

For the vast majority of decisions we face nowadays, it would clearly be better to spend a few more minutes thinking in order to avoid incorrect conclusions. To that end, it’s important to remember how our intuition can fail us, even in easy cases.

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