Question

During the first stages of an epidemic, the number of sick people increases exponentially with time. Suppose that at = 0 days there are 2 people sick. By the time = 3, 40 people are sick. a) Let be the number of sick people at time . Find an exponential equation = expressing in terms of .



b) How many people will be sick by the time = 6?

Answer 1

t = days passed

r = rate of growth

by 0 day, or t = 0, there are 2 folks sick,

$\bf \qquad \textit{Amount for Exponential Growth} \\\\ A=P(1 + r)^t\qquad \begin{cases} A=\textit{accumulated amount}\to &2\\ P=\textit{initial amount}\\ r=rate\to r\%\to \frac{r}{100}\\ t=\textit{elapsed time}\to &0\\ \end{cases} \\\\\\ 2=P(1+r)^0\implies 2=P\cdot 1\implies 2=P\qquad \boxed{A=2(1+r)^t}$

 by the third day, t = 3, there are 40 folks sick,

$\bf \qquad \textit{Amount for Exponential Growth} \\\\ A=P(1 + r)^t\qquad \begin{cases} A=\textit{accumulated amount}\to &40\\ P=\textit{initial amount}\to &2\\ r=rate\to r\%\to \frac{r}{100}\\ t=\textit{elapsed time}\to &3\\ \end{cases} \\\\\\ 40=2(1+r)^3\implies 20=(1+r)^3\implies \sqrt[3]{20}=1+r \\\\\\ \sqrt[3]{20}-1=r\implies 1.7\approx r\qquad \boxed{A=2(2.7)^t}$

how many folks are there sick by t = 6?   $\bf \stackrel{that~many}{A=2(2.7)^6}$