Finger MultiplicationDate: 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/ |
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