A quantity is decreasing exponentially if it decreases by the same percent r in each unit of time t. This is called exponential decay. Exponential decay can be modeled by the equation y C(1 r)t where C is the initial amount (the amount before any decay occurs), r is the decay rate (as a decimal), t represents time, and where 0 < r < 1. The expression (1 r) is called the decay factor.
