A radioactive isotope has a half-life of 10 days. What fraction of a sample remains after 30 days?
Answer and explanation
Correct answer: D. One eighth
- Step 1: 30 days is three half-lives. Step 2. The fraction remaining is (1/2) cubed = 1/8. Answer: one eighth. Why not the others: one quarter is after two half-lives.
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