Path: csiph.com!xmission!news.glorb.com!border1.nntp.dca1.giganews.com!nntp.giganews.com!buffer1.nntp.dca1.giganews.com!nntp.earthlink.com!news.earthlink.com.POSTED!not-for-mail NNTP-Posting-Date: Tue, 20 Jun 2017 09:28:06 -0500 Message-ID: <594930F4.7BE0@ix.netcom.com> Date: Tue, 20 Jun 2017 07:28:04 -0700 From: The Starmaker Reply-To: starmaker@ix.netcom.com X-Mailer: Mozilla 3.04Gold (WinNT; U) MIME-Version: 1.0 Newsgroups: sci.math,sci.physics,sci.physics.relativity,rec.arts.sf.written,alt.astronomy Subject: Re: The Rule Of 72 References: <59441500.660A@ix.netcom.com> <59441500.660A@ix.netcom.com> <59441500.660A@ix.netcom.com> <59441500.660A@ix.netcom.com> <59441500.660A@ix.netcom.com> <59441500.660A@ix.netcom.com> <59441500.660A@ix.netcom.com> <59480DFB.46CB@ix.netcom.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Antivirus: Avast (VPS 170620-2, 06/20/2017), Outbound message X-Antivirus-Status: Clean Lines: 93 X-Usenet-Provider: http://www.giganews.com NNTP-Posting-Host: 108.219.229.47 X-Trace: sv3-EMpxtHnNtisLqF7asjhvex1yQdxWXBSQRn7usORr0ZfXOArziDCFvDD3iGuReVctOg+xoyXCH9qZbjC!2N+C0SZsEg/3ZnqtvsXAKWFajWTL3gHzIrOLmEydhVGgKXi6XqtBhUtfVtUbS0WFQLlCj5qQ0S0l!m+VRqDKQ3dk= X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 X-Original-Bytes: 4474 Xref: csiph.com sci.math:377469 sci.physics:637055 sci.physics.relativity:423117 rec.arts.sf.written:473618 alt.astronomy:291583 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...)