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Re: The Rule Of 72

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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????

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

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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 Dan Christensen <Dan_Christensen@sympatico.ca> - 2017-06-16 11:05 -0700
  Re: The Rule Of 72 William Elliot <marsh@panix.com> - 2017-06-18 00:46 -0700
    Re: The Rule Of 72 Sегgi о <iinvalid@invalid.com> - 2017-06-18 07:03 -0500
      Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-18 13:21 +0000
        Re: The Rule Of 72 Jack Fearnley <jack@alcor.concordia.ca> - 2017-06-18 18:42 +0000
          Re: The Rule Of 72 Sегgi о <iinvalid@invalid.com> - 2017-06-18 14:18 -0500
            Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-19 12:43 +0000
              Re: The Rule Of 72 Sегgi о <iinvalid@invalid.com> - 2017-06-19 08:45 -0500
                Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-20 12:12 +0000
          Re: The Rule Of 72 jmfbahciv <See.above@aol.com> - 2017-06-19 12:43 +0000
            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 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
    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

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