Bismath has half life of 5 days. If sample originally has a mass of $800 \mathrm{mg}$. then the mass…
Bismath has half life of 5 days. If sample originally has a mass of $800 \mathrm{mg}$. then the mass remaining after 30 days will be
$10 \mathrm{mg} .$
$10.5 \mathrm{mg} .$
$12 \mathrm{mg} .$
$12.5 \mathrm{mg} .$
Solution
Original mass $=800 \mathrm{mg}$.
Half life $=5$ days.
We have to calculate remaining mass after 30 days. Understand that $30 \div 5=6$.
$\begin{aligned} \therefore \text { Mass remaining } &=\left(\frac{1}{2}\right)^{6} \times 800 \\ &=\frac{800}{64}=\frac{100}{8}=12.5 \end{aligned}$