Path: utzoo!utgpu!water!watmath!clyde!att-cb!att-ih!ihnp4!ttrdc!levy
From: levy@ttrdc.UUCP (Daniel R. Levy)
Newsgroups: comp.edu
Subject: Re: Mental arithmetic, was: Calculators in exams, was: Becoming CAI literate
Message-ID: <2208@ttrdc.UUCP>
Date: 28 Feb 88 03:43:11 GMT
References: <2032@ukecc.engr.uky.edu> <3900008@nucsrl.UUCP> <24954@cca.CCA.COM>
Distribution: na
Organization: AT&T, Skokie, IL
Lines: 40

In article <24954@cca.CCA.COM>, g-rh@cca.CCA.COM (Richard Harter) writes:
> In article <1988Feb24.224849.928@jarvis.csri.toronto.edu> tjhorton@ai.toronto.edu ("Timothy J. Horton") writes:
> 	If you have a reasonable aptitude for arithmetic, it is faster to do
> the odd multiplication in your head than reaching for a calculator -- if you
> have been trained for quick mental arithmetic.  I amuse myself and startle 
> people by giving the answer to routine calculations while they are still 
> fumbling with the calculator.
> 	I am inclined to think that quick mental arithmetic ought to be
> taught in the schools.

As my own $.02, I found in elementary school that I had the worst problem
with the high-number multiplications (where one or more of the numbers was
greater than 5).  The smaller numbers I could handle by adding in my head.
But the fact that "8 x 7 = 56" for example kept slipping from my mind.

Then from a book of puzzles and games I learned the "finger multiplication"
trick for numbers 6 <= n <=10.  You hold both your hands with the palms
facing you and the thumbs uppermost.  Then you assign the numbers 6 through 10
to the "pinky" through the thumb of each hand, respectively.  To perform
a multiplication between two numbers in this range, touch the tips of
the corresponding fingers together.  Take the sum of the number of fingers
below and including the touching fingers, and multiply that by ten.  Then
add the product of the number of fingers on one side above the touching
fingers and the number of such fingers on the other side.  The result is
the desired multiplication.  For most combinations, the product "above" the
touching fingers will be less than ten, so it's a matter of the tens digit
below, and the units digit above.  The exceptions are 6 x 6 = "twenty-sixteen"
and 6 x 7 = "thirty-twelve" which took some mental addition afterward,
but it still beat rote memorization for me.  Once I knew that trick, I fairly
flew through my arithmetic lessons.  I showed it to a number of my teachers,
none of whom had known it before.

Surely this isn't the only trick around but it sure sounds like a useful one
to teach the munchkins in elementary school who can use all the help they can
get in gettin' down those ole debbil multiplication tables....
-- 
|------------Dan Levy------------|  Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa,
|         an Engihacker @        |  	<most AT&T machines>}!ttrdc!ttrda!levy
| AT&T Computer Systems Division |  Disclaimer?  Huh?  What disclaimer???
|--------Skokie, Illinois--------|