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23. Quick brainteaser to test your cognitive skills…and biases


Brain teas­er: Please con­sider Lin­da, a 31-year-old woman, sin­gle and bright. When she was a stu­dent, in high school and in col­lege too, she was deeply involved in social jus­tice issues, and also par­tic­i­pated in envi­ron­men­tal protests. Which is more prob­a­ble about Linda’s occu­pa­tion today?

a) Lin­da works as a TV reporter;

b) Lin­da is a bank teller;

c) Lin­da is a bank teller, and she’s very active in the envi­ron­men­tal move­ment.


Quick, what’s your answer? a) or b) or c)?

And, in what pre­cise order?



First, ignore how you ranked a), as it is irrel­e­vant to this exer­cise. The key is this: If you ranked c) as more prob­a­ble than b), you are wrong…and in very good com­pany. That’s what most peo­ple tend to answer the first time they face this par­tic­u­lar brain teas­er, and it reflects a very per­va­sive cog­ni­tive bias, tech­ni­cal­ly called a “con­junc­tion fal­la­cy.”

Sta­tis­ti­cal­ly speak­ing, it is more prob­a­ble that Lin­da is a bank teller, which is a whole cat­e­gory, that she is both a bank teller AND also active in the envi­ron­men­tal move­ment, which is a sub­set of the whole cat­e­go­ry of bank tellers.


Next brain teas­er in Sharp­Brains’ top 25 series:

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As seen in The New York Times, The Wall Street Journal, BBC News, CNN, Reuters,  SharpBrains is an independent market research firm tracking how brain science can improve our health and our lives.

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