If originally there were X atoms of radioactive isotope present and now there are only X/16 atoms, how many half-lives have elapsed?

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, after three half-lives X/8, and after four half-lives X/16. Therefore, 4 half-lives have elapsed.

If Originally There Were X Atoms of Radioactive Isotope Present