In this video I look at how a differential equation can be formed from a practical situation. This example uses direct proportion within the question. You will get inverse proportion types as well and I look at these in the next video in this series. Here is the example.

### Example:

- The rate of increase of a certain population P at time t is directly proportional to the population P at time t.
Given that P = 4 when t = 0 and P = 8 when t = 1. Find P when t = 3.