Population Growth Beginning in the next section we will see that differential equations can be used to describeor model many different physical systems. In this problem, suppose that a model of the growing population of a small community is given by the initial-value problem
$$
\frac{d P}{d t}=0.15 P(t)+20, \quad P(0)=100
$$
where $P$ is the number of individuals in the community and time $t$ is measured in years. How fast, that is, at what rate, is the population increasing at $t=0 ?$ How fast is the population increasing when the population is 500 ?