Logistic growth Scientists often use the logistic growth function $P(t)=\frac{P_{0} K}{P_{0}+\left(K-P_{0}\right) e^{-r_{0} t}}$ to model population growth
where $P_{0}$ is the initial population at time $t=0, K$ is the carrying capacity, and $r_{0}$ is the base growth rate. The carrying capacity is a theoretical upper bound on the total population that the surrounding environment can support. The figure shows the sigmoid (S-shaped) curve associated with a typical logistic model.
(FIGURE CAN'T COPY)
The population of the world reached
6 billion in $1999(t=0) .$ Assume Earth's carrying capacity is
15 billion and the base growth rate is $r_{0}=0.025$ per year.
a. Write a logistic growth function for the world's population (in billions), and graph your equation on the interval $0 \leq t \leq 200$ using a graphing utility.
b. What will the population be in the year $2020 ?$ When will it reach 12 billion?