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Re: The Rule Of 72

Cross-posted to 5 groups.

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jmfbahciv wrote:
> 
> [some newsgroups elided]
> 
> The Starmaker wrote:
> > jmfbahciv wrote:
> >>
> >> Jack Fearnley wrote:
> >> > On Sun, 18 Jun 2017 13:21:35 +0000, jmfbahciv wrote:
> >> >
> >> >
> >> >>>
> >> >> But it's a fast way to estimate the time to double the original amount
> >> >> when the interest or dividends are reinvested.
> >> >>
> >> >> IIRC, divide 72 by the percentage.  That will give the number of year to
> >> >> double the original amount.
> >> >>
> >> >> /BAH
> >> >
> >> > The exact doubling time is log(2)/log(1+r/100).
> >> > If we expand log in a Taylor series and take only the first term
> >> > we get the approximate doubling time as 100*log(2)/r.
> >> > That is 69.315/r.
> >> >
> >> > So why don't we use a rule of 69 or a rule of 70?
> >> >
> >> > It turns out that, in the range 1% to 10% and rounded to whole years, 72
> >> > is more accurate than 69.315.
> >> >
> >> > I found this quite surprising.
> >>
> >> There are a lot of accounting tricks having to with 9s.  I suppose people
> >> aren't being taught these rules since most accounting is done by computer
> >> rather than "by hand".  ISTM there was a book published which described
> >> these "9" tricks.  I always meant to figure out proofs for them but
> >> life got in the way :-).  When you first encounter these tricks of the
> >> trade, you think it's magic.
> >>
> >> /BAH
> >
> >
> > You mean like the value someone came up with the speed of light accounting
> trick:
> >
> > 299,792,458 meters per second
> >
> >
> > 299
> >
> >
> >
> > it ends like a 99.9  percent ( how these guys think when they are unsure)
> >
> >
> > 299...just short of 300
> >
> >
> > keeping it under the true value of over 300,000,000.
> >
> >
> >
> > Then I notice other "9" patterns...
> >
> >
> > 299,792,458
> >
> >
> > 792
> >
> > 7+2=9
> >
> > 458
> >
> > 4+5=9
> >
> >
> > 299,792,458 meters per second is an accounting trick, isn't it????
> 
> I'm not talking about numerology.  I'm talking about real accounting
> and bookkeeping practices.  IIRC, one of the "9" tricks helped
> a bookkeeper figure out if an imbalance was caused by transposing
> two numbers.  there were many more little tricks to figure out
> mistakes.
> 
> /BAH

Well, if that is the case then the speed of light should read: 299,792,459


somebody must have made a mistake somewhere...

(i was wondering how that "8" got in there...)

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The Rule Of 72 The Starmaker <starmaker@ix.netcom.com> - 2017-06-16 10:27 -0700
  Re: The Rule Of 72 William Elliot <marsh@panix.com> - 2017-06-18 00:46 -0700
    Re: The Rule Of 72 djheydt@kithrup.com (Dorothy J Heydt) - 2017-06-18 14:07 +0000
      Re: The Rule Of 72 David Bernier <david250@videotron.ca> - 2017-06-18 12:38 -0400
        Re: The Rule Of 72 djheydt@kithrup.com (Dorothy J Heydt) - 2017-06-18 19:27 +0000
    Re: The Rule Of 72 "hanson" <hanson@quick.net> - 2017-06-18 16:07 -0700
    Re: The Rule Of 72 The Starmaker <starmaker@ix.netcom.com> - 2017-06-19 10:46 -0700
      Re: The Rule Of 72 The Starmaker <starmaker@ix.netcom.com> - 2017-06-19 20:01 -0700
      Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-20 12:12 +0000
        Re: The Rule Of 72 The Starmaker <starmaker@ix.netcom.com> - 2017-06-20 07:28 -0700
          Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-21 12:54 +0000
            Re: The Rule Of 72 The Starmaker <starmaker@ix.netcom.com> - 2017-06-21 12:19 -0700
              Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-22 12:28 +0000
                Re: The Rule Of 72 The Starmaker <starmaker@ix.netcom.com> - 2017-06-22 08:58 -0700
                Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-23 11:40 +0000
                Re: The Rule Of 72 The Starmaker <starmaker@ix.netcom.com> - 2017-06-23 10:11 -0700
                Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-24 11:40 +0000
                Re: The Rule Of 72 Valok Planek <lkupuu@kwklewan.oo> - 2017-06-24 11:46 +0000
                Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-25 13:50 +0000
                Re: The Rule Of 72 The Starmaker <starmaker@ix.netcom.com> - 2017-06-24 09:12 -0700
                Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-25 13:50 +0000
        Re: The Rule Of 72 Jack Fearnley <jack@alcor.concordia.ca> - 2017-06-20 14:54 +0000
          Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-21 12:54 +0000

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