Fraction left, or time for a sample or its activity to fall to a fraction, given the half-life

1. A.
   $2 \times 10^{10}$
2. B.
   $7 \times 10^{9}$
3. C.
   $10^{5}$
4. D.
   $4 \times 10^{10}$

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1. A.
   30 days
2. B.
   35 days
3. C.
   40 days
4. D.
   25 days

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1. A.
   7 days
2. B.
   15 days
3. C.
   25 days
4. D.
   35 days

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1. A.
   120 days
2. B.
   130 days
3. C.
   180 days
4. D.
   20 days

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1. A.
   $\frac{1}{8}$
2. B.
   $\frac{1}{2}$
3. C.
   $\frac{1}{4}$
4. D.
   $\frac{1}{16}$

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1. A.
   $3\text{ }T$
2. B.
   $8\text{ }T$
3. C.
   $T$
4. D.
   $2\text{ }T$

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1. A.
   $\frac{1}{8}$
2. B.
   $\frac{1}{4}$
3. C.
   $\frac{7}{8}$
4. D.
   $\frac{3}{4}$

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