If a radioactive isotope that was injected into your bloodstream has a half life of 5 hours, how many hours do you have to wait before the amount of this isotope in your body is $ \frac{1}{16} $ its original amount?
A) 20
B) 25
C) 5
D) 10
E) 15

Question

Quizplus · Accepted Answer

The amount of a radioactive isotope decreases by half every half-life. To reach $ \frac{1}{16} $ of the original amount, it must go through 4 half-lives because $ \frac{1}{16} = \left(\frac{1}{2}\right)^4 $. Since each half-life is 5 hours, 4 half-lives take 20 hours.

If a Radioactive Isotope That Was Injected into Your Bloodstream 116 \frac{1}{16} 161​

If a Radioactive Isotope That Was Injected into Your Bloodstream $\frac{1}{16}$