A very tricky finger trick

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**You can create:**

- Extensions of the multiplication finger system into other bases, or larger numbers
- A theory of why it works

**How?**

The video above describes a finger trick that works for times tables from 6 to 10 - if you remember the times tables up to 5. Your quest, of course, is figure out why it works. Try to draw charts on graph paper, use counters and other problem-solving techniques.

Can you modify this trick to work in different number bases? Can two people join forces and do multiplication up to 20 on their four hands? These are less obvious (and not so pretty and easy) extensions, but I played with them before with some success.

**Why?**

Because this finger trick is almost like magic!

**As you go**

- Head to youtube.com for more amazing math finger tricks. It's a treasure trove.

**Higher and deeper**

- Figuring out why tricks work leads directly into algebra.
- There are some pretty complicated finger math systems out there. All of them are based on algebra and number theory ideas.