population: 2,100 bacteria
petri dish radius : 40 millimeters
Area of a circle = π r²
A = 3.14 * (40mm)²
A = 3.14 * 1,600 mm²
A = 5,024 mm²
Population density is the measurement of the population per unit area or unit volume:
population / area = 2,100 / 5,024mm² = 0.41799
The approximate population density is 0.42 bacteria per square millimeter
