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Q&A #5245


Multiplication with your ten fingers

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From: Gail (for Teacher2Teacher Service)
Date: Nov 30, 2000 at 21:24:32
Subject: Re: Multiplication with your ten fingers

Here is what you do.   Hold your two hands up in front of you with the
palms facing you.  Then number the fingers of the hand like this:

thumbs are "6"
index fingers are "7"
middles are "8"
ring fingers are "9"
little fingers are "10"

To multiply two of those numbers (6 through 10 ) together, you touch the
finger tips of the two numbers.  So, if you wanted to multiply 7 X 8, you
would touch the 7 finger of one hand to the 8 finger of the other.

You hands would look something like this:

          6       6
                  7
                78          the 7 and 8 are touching, but all the other
               8   9               fingers are free
              9      10
            10
Count the number of fingers ABOVE the touching fingers (in this case there
are 3, of them). Add the two touching fingers to this total. (3 + 2 = 5)
Multiply that number by ten, and remember it (so, in this case, remember
"50")

Now count the number of fingers below the touching fingers on EACH hand...
like this:  there are 3 on the left hand, and there are 2 on the right hand.
Multiply these two numbers together. (In this case, 3 X 2 = 6) Add that
product to the number you got for the top fingers ("50"), and that is the
product of the two numbers...   50 + 6 = 56.


Let's try one more...  how about 6 X 7

                     6
                 67
                7   8          the 6 and 7 are touching, but all the other
               8      9               fingers are free
              9        10
            10

1 finger ABOVE, plus the two touching fingers, is three fingers. 3 X 10 = 30

4 fingers on the left hand, times 3 fingers on the right hand. 4 X 3 = 12

30 + 12 = 42, and that is the product of 6 X 7.


Now that I have told you all that, I will also throw in my two cents' worth
about number sense.  This "trick" will not teach your students number sense.
They would really be better off making arrays, and sets of numbers to "see"
the different products.  They can build upon those experiences later.  The
finger trick can be time-consuming and does not transfer to conceptual
understanding.

 -Gail, for the T2T service

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