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Neurology Now:
doi: 10.1097/01.NNN.0000412273.71200.83
Departments: The Waiting Room

Neurobics: Sock Logic

Kim, Scott

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scott@scottkim.com

Use your logic skills to find matching pairs of socks.

1. In a pitch-black room, you reach your arm into a box containing 10 black socks and 10 white socks. What is the smallest number of socks you need to take with you in order to make sure you have at least one pair of matching socks when you step out of the room into the light?

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2. In a pitch-black room, you reach your arm into a box containing 10 black socks, 10 red socks, and 10 white socks. What is the smallest number of socks you need to take with you to make sure you have at least two pairs of matching socks when you step out of the room into the light?

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3. In a lighted room, you see three boxes labeled “Black,” “White,” and “Black & White.” One box contains just black socks, one contains just white socks, and one contains both, but the labels have been scrambled so that all three boxes are mislabeled. Figure out how to place all the labels correctly by pulling just one sock out of just one box. No peeking into the boxes. Which box should you reach into, and how can you figure out what the labels should really be?

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These puzzles was adapted from the book The Playful Brain: The Surprising Science of How Puzzles Improve Your Mind, by Richard Restak and Scott Kim (Riverhead Books 2010). For more information, visit theplayfulbrain.com.

Scott Kim

©2012 American Academy of Neurology

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