## 10.3 Outline

- Growth/decay formula
- Population growth
- Radioactive decay
- Logarithmic scales
- Richter number
- Richter scale
- decibel
- decibel formula

## 10.3 Essential Ideas

Exponential **growth **or **decay **can be described by the equation

*A*=*A _{o}e^{rt}*

where *r *is the annual growth/decay rate, *t *is the time (in years), *A _{o }*is the amount present initially (present value) and

*A*is the future value. If

*r*is positive, this formula models growth and if

*r*is negative, the formula models decay.