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From: tlh@cs.purdue.EDU (Thomas L. Hausmann)
Newsgroups: comp.edu
Subject: Re: Mental arithmetic was: Calculators in Exams
Message-ID: <3337@arthur.cs.purdue.edu>
Date: 28 Feb 88 04:48:07 GMT
References: <2032@ukecc.engr.uky.edu> <3900008@nucsrl.UUCP> <24997@cca.CCA.COM>
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Organization: Department of Computer Science, Purdue University
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In article <24997@cca.CCA.COM>, g-rh@cca.CCA.COM (Richard Harter) writes:
> In article <7301@tut.cis.ohio-state.edu> zwicky@pterodactyl.cis.ohio-state.edu (Elizabeth D. Zwicky) writes:
> > ...
> >up was that he was doing cross-multiplication, just like the books have
> >you do. That gets good scores on tests, because it looks right. I
> >was moving the decimal place to get 10% and then multiplying that,
> >which math teachers fail because the intermediate steps aren't "right"
> >but it sure works.)			
> 	One question -- what did you mean by cross multiplication.  To
> me, this means the following method.  Example:
> 	523
> 	469
> 	---
>      245287
> <two methods given for hand solution> 


I use a mental chalkboard and visualize myself working the problem by hand.
i.e.  523
      469
      ---
     4707
    3138 
   2092
   ------
   245287

One's capacity to do this is probably limited.  I haven't "pushed it" to see
how big of numbers I can handle.


-------------------------------------------------------------------------------
Tom Hausmann       Dept. of Computer Sciences     Purdue University
tlh@mordred.cs.purdue.edu    | My ideas?  There has never been an original
...!purdue!tlh               | thought since Plato.