A radioactive sample decays from 80 grams to 10 grams over a period of 12 hours. What is its half-life?
Answer and explanation
Correct answer: C. 4 hours
- Step 1: 80 -> 40 (1 half-life) -> 20 (2 half-lives) -> 10 (3 half-lives). Step 2. 3 half-lives = 12 hours => 1 half-life = 12 / 3 = 4 hours. Answer: 4 hours. Why not the others: 6 hours corresponds to only 2 half-lives (80 to 20 grams).
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