# Applications of Exponential Functions

## Word problems with variables as exponents

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Practice Applications of Exponential Functions

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It's Epidemic

Credit: Lucia Sanchez
Source: http://www.flickr.com/photos/12477719@N00/3049994994/

One person with an illness can kill millions. How? By starting an epidemic. When a person contracts a new disease, the disease spreads exponentially. Each person she infects makes many other people sick. Soon, the disease can rage out of control.

#### Epidemic, Pandemic, Plague!

Diseases are transmitted quickly because the people who have them are contagious before they start feeling sick. That means they walk around and infect other people for several days before they notice symptoms of their illness. Those people then infect more people. The cycle continues, with more and more people falling sick with each wave of the disease. When an epidemic spreads to multiple countries or regions, it becomes a pandemic, which means that the whole world is at risk. Some epidemics are fairly mild. Many people get sick, but they don’t die. However, some diseases are extremely virulent. This means that they kill a high percentage of their victims. In the past, the bubonic plague, polio, and swine flu all proved to be dangerous epidemics. In the modern United States, epidemics tend to kill very few people, but in developing countries death from disease remains a constant risk.

Credit: Blake Patterson
Source: http://www.flickr.com/photos/35448539@N00/4919795171/

Public health workers have several tools to stop epidemics. Vaccinations make people immune to the disease, which means they cannot catch it or pass it on. If health workers can vaccinate many people very quickly, they may be able to stop the disease in its tracks. In emergencies, some communities quarantine sick people. This prevents people with the disease from touching or breathing on people who are healthy. However, because many people are contagious before they show symptoms, quarantine often fails to contain the disease’s spread. Recently, scientists have studied ways to use social networks—both real-life and digital—to stop disease. In the next pandemic, Twitter and Facebook may help keep people healthy and safe.

#### Explore More

At the links below, follow the spread of the ongoing cholera epidemic that originated in Haiti in 2010.

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