Answer:
Explanation:
1) Half-life is the time for the decay of a sample of matter to half its initial amount.
2) Radioisotopes (radioactive isotopes), such as strontium-90, have constant half-life times.
3) You can relate the time a radioactive samplle has been decaying with the percent of the matter remaining and the number of half-lives elapsed:
[tex][A]/[Ao]=(1/2)^n[/tex]
Where [A]/[Ao] is the ratio ratio of final amount to initial amoun, and n is the number of half-lives elapsed.
Here, n = 100 years / 28.1 years ≈ 3.559
Then:
[tex][A]/[A_0]=(1/2)^{3.559}=0.08486[/tex]
And the percent is 100 × 0.08486 = 84.86% = 84.9 %
