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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 
about this process and/or a site to find 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
  answer!

Pat Willette tells you more about this method here:

  http://www.megalink.net/~jones/chisanbop.html   


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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