A petri dish is simply a circle; thus, we use the formula of the area of the circle which is <span>πr^2. Given r = 40 mm A = </span>π(40)^2 = <span>5026.55 sq. mm </span> Population density = bacteria count / area PD = 2,100 / <span>5026.55 PD = </span><span>0.417782 bacteria / mm sq.
Therefore, the answer is approximately 0.418 </span><span>bacteria per square millimeter.</span>
Determine the area of the circular petri dish through the equation, A = <span>πr^2. Substituting the radius to the equation and solving for area gives, 5024 mm^2. The population density is obtained by dividing the population with the calculated area. Thus, the population density is approximately 0.418 bacteria per mm^2. </span>
