We know that the half life of this element is 41.3 days.
We have to find how much will remain of a sample of 2 grams after 86 days.
The half life of 41.3 days means that the mass after 41.3 days will become half of what it was.
We can express this as:
[tex]\frac{M(t+41.3)}{M(t)}=\frac{1}{2}[/tex]
As this is represented with an exponential model like this:
[tex]M(t)=M(0)\cdot b^t[/tex]
we can use the half-life to find the parameter b:
[tex]\begin{gathered} \frac{M(t+41.3)}{M(t)}=\frac{1}{2} \\ \frac{M(0)\cdot b^{t+41.3}}{M(0)\cdot b^t}=\frac{1}{2} \\ b^{t+41.3-t}=\frac{1}{2} \\ b^{41.3}=\frac{1}{2} \\ b=(\frac{1}{2})^{\frac{1}{41.3}} \end{gathered}[/tex]
Then, knowing that the initial mass M(0) is 2 grams, we can express the final model as:
[tex]M(t)=2\cdot(\frac{1}{2})^{\frac{t}{41.3}}[/tex]
We then can calculate the mass after t = 86 days as:
[tex]\begin{gathered} M(86)=2\cdot(\frac{1}{2})^{\frac{86}{41.3}} \\ M(86)\approx2\cdot0.236 \\ M(86)\approx0.472 \end{gathered}[/tex]
Answer: the mass after 86 days will be 0.472 grams.
