Question

Soon after taking an aspirin, a patient has absorbed 320 mg of the drug. After 2 hours, only 80 mg remain. Find an exponential model for the amount of aspirin in the bloodstream after t hours.

Answer 1

`\bf \qquad \textit{Amount for Exponential Decay}\\\\ A=I(1 - r)^t\qquad \begin{cases} A=\textit{accumulated amount}\\ I=\textit{initial amount}\\ r=rate\to r\%\to (r)/(100)\\ t=\textit{elapsed time}\\ \end{cases}\\\\ -------------------------------\\\\ \textit{at 0 seconds, t = 0, the patient has 320mg in its blood} \\\\\\ 320=I(1-r)^0\implies 320=I\cdot 1\implies 320=I \\\\\\ A=320(1-r)^t\\\\ -------------------------------\\\\`


`\bf \textit{2 hours later, t = 2, the patient has 80mg in its blood} \\\\\\ 80=320(1-r)^2\implies \cfrac{80}{320}=(1-r)^2\implies \cfrac{1}{4}=(1-r)^2 \\\\\\ \sqrt{\cfrac{1}{4}}=1-r\implies \cfrac{√(1)}{√(4)}=1-r\implies \cfrac{1}{2}=1-r\implies r=1-\cfrac{1}{2} \\\\\\ r=\cfrac{1}{2}\implies r=0.5\qquad A=320(1-0.5)^t\implies \boxed{A=320(0.5)^t}`