Posted by Elizabeth on April 7, 2002, at 22:31:29
In reply to JohnX2: how does this work in reverse: » JohnX2, posted by Janelle on April 5, 2002, at 19:50:32
> You wrote "For 1/32 you DO need exactly 5 half lives."
>
> How do you go from 1/32 to get the 5 (for number of half lives)2^5 = 2 x 2 x 2 x 2 x 2 = 32
2^(-5) = 1/(2^5) = 1/32 = 0.03125 = 3.125%
Someone just must have decided that 3% or so was a nice cut-off for "gone." It's just a matter of where you draw the line, not a law of nature.
(Like I said, 7 half-lives -- by which time 1/128, less than 1%, remains -- is what I was taught.)
-elizabeth
poster:Elizabeth
thread:101843
URL: http://www.dr-bob.org/babble/20020402/msgs/102330.html