Yeast Growth The amount $Y$ of yeast in a culture is given by the model
$$Y=\frac{663}{1+72 e^{-0.547 t^{\prime}}}, \quad 0 \leq t \leq 18$$
where $t$ represents the time (in hours).
(a) Use a graphing utility to graph the model.
(b) Use the model to predict the populations for the 19 th hour and the 30 th hour.
(c) According to this model, what is the limiting value of the population?
(d) Why do you think the population of yeast follows a logistic growth model instead of an exponential growth model?