Question

After 8 yr there will be ?g of a radioactive substance

Answer 1

$\begin{gathered} 9=18e^{-3k} \\ 0.5=e^{-3k} \\ ln(0.5)=-3k \\ k=-\frac{ln(0.5)}{3}=0.23105 \end{gathered}$

Thus;

$\begin{gathered} A=18e^{-0.23105\times8} \\ A=2.835 \end{gathered}$

Thus, the remaining amount is 2.835 g