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

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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?

.

Solution

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.

Right?

Next brain teas­er in Sharp­Brains’ top 25 series:

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