If you were to add two goldfish into a fish tank that already contains three goldfish, explain what happens to the population density of then fish tank.

Population density is how many people live in one area. So if you have one square mile and there are 100 people there, and another square mile area with 1,000 people then the second area has a higher population density, because there are more people condensed into that one area. If you add two goldfish to the already existing 3 goldfish, population density increases because there are more fish in one condensed area.