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?

Answer 1

Since (1/2)^4 = 1/16, that would require 4 half-lives, which is 5 billion years.

Answer 2

5 billion

Answer 3

5bil

Answer 4

2.5 billion