Answer: [tex]26.4\ \text{days}[/tex]
Step-by-step explanation:
Given
Half life of radioactive substance is [tex]T_{\frac{1}{2}}=20\ \text{days}[/tex]
Initial amount [tex]A_o=2\ \text{days}[/tex]
Amount left at any time is given by
[tex]\Rightarrow A=A_o2^{\dfrac{-t}{T_{\frac{1}{2}}}}\\\\\Rightarrow 2=52^{\dfrac{-t}{20}}\\\\\Rightarrow 0.4=2^{\dfrac{-t}{20}}\\\\\Rightarrow 2^{\dfrac{t}{20}}=2.5\\\\\Rightarrow \dfrac{t}{20}\ln 2=\ln (2.5)\\\\\Rightarrow t=\dfrac{20\ln (2.5)}{\ln 2}\\\\\Rightarrow t=26.4\ \text{days}[/tex]
It takes 26.4 days to reach 2 gm.
