Chapter 4.1, Problem 69ES

Suppose that the spread of a flu virus on a college campus is modelled by the function $y\left(t\right)=\frac{1000}{1+999e^{-09t}}$ where, $y\left(t\right)$ is the number of infected students at time $t$ (in days, starting with $t=0$ ). Use a graphing utility to estimate the day on which the virus is spreading most rapidly.