• # question_answer A radioactive isotope has a half-life of 10 days. What was its original weight 40 days earlier if today it is$125\text{ }g$? A)  $600\text{ }g$                       B) $1000\text{ }g$ C)  $1250\text{ }g$                     D) $2000g$

${{t}_{{\scriptstyle{}^{1}/{}_{2}}}}=10$ days $T=40$ days $n=\frac{T}{{{t}_{{\scriptstyle{}^{1}/{}_{2}}}}}=\frac{40}{10}=4$ $\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}={{\left( \frac{1}{2} \right)}^{4}}$ $\frac{125}{{{N}_{0}}}=\frac{1}{16}$ ${{N}_{0}}=2000g$