A 40gm radioactive material is placed in a chamber, having a half-life of 20 days. How much will be left after 80 days?
Answer: 2.5gm
Explanation
After 1 half-life (20 days), the amount left is 40/2 = 20gm.After 2 half-lives (40 days), the amount left is 20/2 = 10gm.
After 3 half-lives (60 days), the amount left is 10/2 = 5gm.
After 4 half-lives (80 days), the amount left is 5/2 = 2.5gm.
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