On 2005-07-27, DanielLee <firstname.lastname@example.org> wrote: > $1,000 usd @ 10.683 = $10,682.750 pesos > > When I am converting pesos to dollars the exchange rate is shown like > this > > $10,682 pesos @ 0.09361 = $999.92980 dollars > > I know that the exchange rate may be different for each conversion > depending on currency values or what ever. I was figuring that the > dollar to peso number of 10.683 could lead me to the number I needed if > I wanted to convert pesos to dollars at the same rate. > > It seems that since a dollar to peso rate of 10.000 is equal to a pesos > to dollar rate of 0.10000. Or stated another way (10 before the decimal > point was equal to 10 after the decimal point) then a 10.5000 number > before the decimal point would equal a .09500 (or some such number) > after the decimal point. That the addition to one would equal the > subtraction from the other. But when I do it that way it does not work.
Indeed it does not. 1/10.5 is approximately 0.95238 (more precisely, it is 0.95238095238095238...).
> What I would like to know now is how do I do the math to get the > inverse number?
The multiplicative inverse of a number is 1 divided by the number. (Technically, this statement is a bit backward, as division is defined as multiplication by the multiplicative inverse, but the basic idea, that multiplying a number by its multiplicative inverse gives you 1, is the key point.)
So if you have 10.5 pesos per dollar, you have 1/10.5 dollars per peso.
You really only need one exchange rate (if there is no markup or commission being computed). You then multiply by the exchange rate to do the conversion in one direction, and divide by it to do the conversion in the other direction.
$1000 * 10.5 pesos/dollar = 10,500 pesos
10,500 pesos / 10.5 pesos/dollar = $1000
------------------------------------------------------------ Kevin Karplus email@example.com http://www.soe.ucsc.edu/~karplus Professor of Biomolecular Engineering, University of California, Santa Cruz Undergraduate and Graduate Director, Bioinformatics (Senior member, IEEE) (Board of Directors, ISCB) life member (LAB, Adventure Cycling, American Youth Hostels) Effective Cycling Instructor #218-ck (lapsed) Affiliations for identification only.