## Summary:

- Populations gain individuals through births and immigration.
- They lose individuals through deaths and emigration.
- These factors together determine how fast a population grows.
- The formula for population growth takes all these factors into account.
- The two main factors affecting population growth are the birth rate (b) and death rate (d) Population growth may also be affected by people coming into the population from somewhere else (immigration, i) or leaving the population for another area (emigration, e) The formula takes all of these factors together to determine the population growth rate.

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