Option: C is the correct answer.
C. 18.51 g
The situation of this problem can be modeled with the help of the exponential decay function :
i.e. any component if it has a initial amount as a units and is decaying at a rate of r% then the amount after t years is given by:
[tex]n(t)=a(1-\dfrac{r}{100})^t[/tex]
Here we have:
r=13%
and a=300 g
and t=20 years
Hence, we have
[tex]n(20)=300\cdot (1-\dfrac{13}{100})^{20}\\\\i.e.\\\\n(20)=300\cdot (1-0.13)^{20}\\\\i.e.\\\\n(20)=300\cdot (0.87)^{20}\\\\n(20)=300\cdot 0.061714\\\\i.e.\\\\n(20)=18.5142\ g[/tex]
The amount that will be left after 20 years is: 18.51 g
