Explanation:
The dunction is given below as
[tex]A(t)=100(1.3)^{-t}[/tex]To figure out the half life,
The new mass of the decayed substance will be half that of the initial substance
[tex]\begin{gathered} A(t)=100\left(1.3\right)^{-t} \\ A(t)=\frac{100}{2}=50 \end{gathered}[/tex]By substituting the values, we will have
[tex]\begin{gathered} A(t)=100(1.3)^{-t} \\ 50=100(1.3)^{-t} \\ \frac{50}{100}=1.3^{-t} \\ \frac{1}{2}=1.3^{-t} \end{gathered}[/tex]Apply exponent rules
[tex]\begin{gathered} \frac{1}{2}=1.3^{-t} \\ ln(\frac{1}{2})=-tln(1.3) \\ t=\frac{ln(2)}{ln(1.3)} \\ t=2.64years \end{gathered}[/tex]Hence,
The final answer is
[tex]2.64years[/tex]