
Re: Great Math Tricks on youtube
Posted:
Jan 1, 2014 9:36 AM


Am 01.01.2014 01:31, schrieb Christopher J. Henrich: > In article <79fe4482109f4177b73aeee98fa1dff8@googlegroups.com>, > christian.bau <christian.bau@cbau.wanadoo.co.uk> wrote: > >> On Monday, December 30, 2013 8:37:29 AM UTC, Phil Carmody wrote: >>> Today I learnt that >>> >>> 11.5 / 2 = 6.725 >>> >>> Teach me more of these internet things called "math tricks"! >> >> Sad that the guy is really bad at mental arithmetic. >> >> Apart from that, he tells us that to solve (1 + p / 100)^n = 2 for n we let n >> = 72 / p, > A better approximation is 69/p, based on ln(2) = 0.693...
Of course this is a better approximation for very small values of p, but they are not of very high interest for an investor ;) For values of p between let's say p=5% and p=20% the 72rule seems to work better.
 Thomas Nordhaus

