The half life formula is
[tex]m=m_0(\frac{1}{2})^{\frac{t}{th}}[/tex]where m0 is the amount started with, m is the amount left after a time t and th is the half life.
In our case
[tex]\begin{gathered} m_0=16\text{ gr} \\ t_h=7\text{ days} \end{gathered}[/tex]Hence, we obtain:
a) After 7 days
[tex]\begin{gathered} m=(16)(\frac{1}{2})^{\frac{7}{7}} \\ m=16(\frac{1}{2}) \\ m=8\text{ gr} \end{gathered}[/tex]b) After 14 days
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