**Learning objectives**

- Gain familiarity with area densities and their units
- population: people per square mile
- mass: kg per square meter
- flow: gallons/second per square meter, kg/sec per square meter

- Express the solution to a density problem using integral notation
- Work with integrals of densities
- Understand a double integral as a sum with units

**Before class**

- Reading
- Ponder problems from the reading: 16.1: 1, 3, 5, 7, 15.
- Consult the main points of the lesson

**In class**