If originally there were X atoms of radioactive isotope present and now there are only X/8 atoms, how many half-lives have elapsed?

Name: If originally there were X atoms of radioactive isotope present and now there are only X/8 atoms, how many half-lives have elapsed?
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Question

Quizplus · Accepted Answer

Each half-life reduces the number of atoms by half. Starting with X atoms, after one half-life, there would be X/2 atoms, after two half-lives, X/4 atoms, and after three half-lives, X/8 atoms.

If Originally There Were X Atoms of Radioactive Isotope Present