 Scientists estimate that on Halloween 2011 the global population reached 7 billion. But how long did it take humanity to grow to this level, and how large should we expect our population to become?

In this lesson, students will explore how many people the Earth is adding and losing each minute, and use this to build an exponential model for human population growth. They’ll also predict what the world population will be in the future and discuss the environmental consequences of population growth and economic development.

### Students will

• Given two data points, calculate growth rate as a percent
• Build and evaluate an exponential function in a real-world context
• Analyze graphs showing roughly exponential relationships

### Before you begin

Students should be familiar with calculating percent change, as percent growth will be the basis for the entire lesson. Because they will need to model growth in order to make predictions about future population numbers, students should also be able to write an exponential function given a starting value and growth rate.