*Post by The Starmaker**Post by jmfbahciv**Post by Jack Fearnley*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

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...