There are 20 goldfish in a pond. Their population is increasing by 20% each year. The same pond has 100 minnows. The minnow population is increasing by 10 minnows each year. Make a graph to find the year that the two species of fish will have the same population. In what year will the fish populations be approximately the same?

The graph is attached, showing the intersection point at 13.5 years and populations of 235.2 for each population.

We only consider the portion of the graph from x=0 on, since negative time is illogical.  Tracing the graph we get the intersection point.