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Re: The Rule Of 72

Cross-posted to 5 groups.

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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????


Okay...going a step further on the "9" accounting trick..

How many nines are there in  299,792,458?

There are three numbered "9"'s
There are 4+5=9 and 7+2=9 2+7=9
So that totals 3 more "9"s
Then you have nine digits - 299,792,458


299,792,458 meters per second is an accounting trick, isn't it????


What is the speed of light? 99999999999999999999999998


good thing i'm not good at arithmetic...

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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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