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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:

  • #24. A few guesstimations often used in consulting and tech interviews

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