Question

RS1 remaining parent material is 12.5%. RS2 remaining parent material is 25%. Based on the amount of remaining parent material in the rocks, how many half-lives have occurred for each?

Answer 1

$RS1:\;\;(\frac{1}{2})^n=0.125=\frac{1}{8} \;\; ->\;\; n=3.\;\;3\;half-lives\;occured.\\ RS2:\;\;(\frac{1}{2})^n=0.25=\frac{1}{4} \;\; ->\;\; n=2.\;\;2\;half-lives\;occured.$