There are 2,100 bacteria in a circular petri dish. The dish has a radius of 40 millimeters. What is the approximate population density? (Use 3.14 for π)Area of a circle = πr2

The dish’s area is 3.14 × 40² = 3.14 × 1,600 = 5,024 square millimeters. Divide the 2,100 bacteria by 5,024 square millimeters: 2,100 ÷ 5,024 ≈ 0.42 bacteria per square millimeter. The correct choice is 0.42 bacteria per square millimeter.

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