Homework Help: earth space science

Posted by Potassium-40 has a half-life of approximately 1.25 on Thursday, February 9, 2012 at 9:53am.

Potassium-40 has a half-life of approximately 1.25 billion years. Approximately how many years will pass before a sample of potassium-40 contains one-sixteenth the original amount of parent isotope?

earth space science - drwls, Thursday, February 9, 2012 at 10:20am
Since (1/2)^4 = 1/16, that would require 4 half-lives, which is 5 billion years.

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