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### Finger Multiplication

```
Date: 04/18/97 at 21:58:53
From: Anonymous
Subject: finger math

I listened to a discussion by a Visual Impaired Specialist.  She
talked about using "finger math" to teach blind children math, and
said it worked for seeing students as well. I would like information
```

```
Date: 04/19/97 at 11:30:04
From: Doctor Sarah
Subject: Re: finger math

Hi -

Here's information on a finger-calculator method
called chisanbop:

Place your hands palm-down on a table, fingers spread.
That's zero. Now make two fists. Your calculator now
reads 99, the highest value. Reading from left to right
now, each of the four fingers on your left hand equals
ten; the left thumb equals fifty; the right thumb equals
five; and each of the four fingers on your right hand
equals one. Now construct different numbers on your own.
Two thumbs folded under could only equal 55; two index
fingers, 11.

Let's try a sample problem: 18 + 26. Show 18 by pressing
down the left index finger and the right thumb, index,
middle, and ring fingers.

Now: Think of 26 as 10, 10, 5 and 1. The first two 10s
are easy: Press down the middle and ring fingers on
your left hands. The 5 is the only tricky part; you
exchange between hands. Lift the right thumb
(subtracting 5), then press down your left pinky
(adding 10, for a net gain of 5). For the 1, press down
the right pinky. Your hands now read 44--the correct

And here's a finger multiplication method for one-digit
numbers greater than 5, from the sci.math newsgroup:

From: rusin@washington.math.niu.edu (Dave Rusin)
Newsgroups: sci.math
Subject: Re: Trachtenberg Math
Date: 21 Mar 1995 03:40:02 GMT

...

In this category I'll toss out the following method for
multiplying one-digit numbers greater than  5.

On each hand, label your fingers "6" thru "10" (yes, I know
that's not a one-digit number) from the thumb outwards.
To multiply two of these numbers together, place together
the corresponding fingers from the two hands and read off
the two-digit answer as follows:

- the first digit is the number of fingers from thumb to
thumb, crossing over from one hand to the other where the
fingers touch. (Don't forget to count the touching fingers
as well).

- the second digit of the answer is the product of the
numbers of fingers not yet counted on each hand.

Example: to compute 7 x 8, touch the left index finger to the
right middle finger. Count left thumb, left index, right middle,
right index, right thumb: 5 fingers. Now multiply 3 (middle,
ring, pinky on left) times 2 (ring and pinky on right) to get
the second digit, 6.

The results are accurate for {6,...,10} x {6,...,10}, although
the cases 6 x 6 and 6 x 7 need to be properly interpreted.

This is not "accidental"; it works for n-fingered beasts who
count base  n (as long as they have those fingers on precisely
two hands!).

-Doctor Sarah,  The Math Forum
Check out our web site!  http://mathforum.org/dr.math/
```
Associated Topics:
Elementary Multiplication

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