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Neurology Now:
doi: 10.1097/01.NNN.0000361352.23273.63
Department: the Waiting Room

Neurobics: Sum Snap

Kim, Scott

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Here's a puzzle that will have you juggling numbers in your head. The picture below shows numbers in circles. Your challenge is to find chains of numbers that add up to 10. Each number in the chain must connect to a neighboring number, moving one step horizontally, vertically, or diagonally. For instance, the gray line passes through four numbers 3–2–1–4, which add to 10.

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NOW IT'S YOUR TURN

Figure. No caption a...
Figure. No caption a...
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1. How many different chains of two circles can you find that add to 10? For instance, can you find the chain 7–3?

2. How many chains of same-colored circles can you find that add up to 10? The chains can be any length. For instance, can you find the same-colored chain 5–3–2?

3. What is the longest chain you can find that adds to 10?

4. How many chains of three circles can you find that add up to 10? Count two chains as the same if they have the same circles, even if they are connected in a different order.

This puzzle is based on Sum Snap, a computer game made by FitBrains. Like other brain fitness companies, FitBrains offers games that exercise different parts of your brain, just like a gym offers machines that exercise different parts of your body. To play Sum Snap and other brain exercise games, visit FitBrains.com.

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NEUROBICS ANSWER

Scott Kim

Figure. COURTESY SCO...
Figure. COURTESY SCO...
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©2009 American Academy of Neurology

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