Re: [Fwd: [MATHEDCC] Number theory question]

Martha Haehl (haehl@KCMETRO.CC.MO.US)
Wed, 10 Feb 1999 21:47:43 -0500

Thanks everyone for the responses on the number theory question. I had
heard of casting out nines, but I guess had never worked with it. I loved
the review of modular arithmetic which I have not worked with for quite some
time. Like one person said, I did not have time for this problem, but the
interest in it snuck in and grabbed me and I guess the love for mathematics
won out and side-tracked me momentarily from the work I am supposed to be
doing to meet some deadlines.

Martha

-----Original Message-----
From: John Gann <john@mail.fm>
To: Subscribers MATHEDCC <mathedcc@archives.math.utk.edu>
Date: Wednesday, February 10, 1999 6:26 PM
Subject: [Fwd: [MATHEDCC] Number theory question]

>This question/examples sounds like what we used to do in 3rd
>and 4th grade at one school I attended. We called the
>process, "casting out nines." We were required to use this
>method to check our arithmetic work (I suspect it was also
>to improve a arithmetic skills). The method worked like
>this:
>
>Add the following numbers: 2637 + 3815 = 6452
>
>Now apply the "casting out nines" check. Add the digits of
>each number together. While adding, if you equal or exceed
>9, subtract 9 and continue.
>
>(2+6)+3 = 11, caste out nine
>11-9=2, continue
>2+7=9, caste out nine
>9-9=0
>
>So, next to 2637 we write 0.
>
>For 3815, we would write 8.
>
>For 6452, we would write 8.
>
>Our check, then, is 0 + 8 = 8.
>
>We did this for all our arithmetics homework and classwork.
>
>--
>John R Gann
>
>College of Micronesia - FSM
> PO Box 159
> Pohnpei, FM 96941
>AOL Instant Messenger: Mathletics
>Homepage:
>http://ourworld.compuserve.com/homepages/mathlete/home.htm
>
>"Tough guys don't do math. Tough guys fry chicken for a
>living."
> - Jaime Escalante (as portrayed in "Stand and
>Deliver")
>
>

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