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Re: The Rule Of 72

Cross-posted to 3 groups.

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On 6/18/2017 1:42 PM, 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.
> 
> Best regards,
>               Jack Fearnley
> 
> 



I got this confused with the Rule of 78 used with Loans,

http://www.tiac.net/~mabaker/rule_of_78.html

it replaced simple interest calculation in the 60's and 70's and
it made you pay more for a loan

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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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