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A radioactive substance has a half-life of 20 days what fraction the original radiation ...

A radioactive substance has a half-life of 20 days what fraction the original radiation nuclei will remain after 80 days?
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  • A (1)/32
  • B (1)/16
  • C (1)/ 8
  • D (1)/4
Correct Answer: Option B
Explanation:
80 days = 4 half lives (i.e 4 x 2odqs = 80 days)
But the fraction always left by any radioactive material after 4half lives is (1/2)4 = (1)/16

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