Half-life from the fraction of a sample left after a given time

1. A.
   $5sec$
2. B.
   $\frac{4}{3}\sec$
3. C.
   $2.5sec$
4. D.
   $7.5sec$

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1. A.
   20 years
2. B.
   10 years
3. C.
   40 years
4. D.
   5 years

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1. A.
   9.5 years
2. B.
   8.5 years
3. C.
   7.5 years
4. D.
   10.5 years

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1. A.
   $5\text{ }\min$
2. B.
   $7.5\text{ }\min$
3. C.
   $15\text{ }\min$
4. D.
   $30\text{ }\min$

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1. A.
   $64\text{ }g$
2. B.
   $40\text{ }g$
3. C.
   $32\text{ }g$
4. D.
   $256\text{ }g$

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