Example

Example: Evaluating an Exponential Decay Model for a Bacteria Population

To evaluate an exponential decay model, first determine the decay rate, and then apply it to find a future amount. For example, suppose a bacteria population declines from 700,000 to 400,000 in 5 hours after the administration of medication. Using the exponential decay formula A=A0ektA = A_0 e^{kt}, substitute the given values: 400,000=700,000ek5400{,}000 = 700{,}000 e^{k \cdot 5}. Dividing by 700,000 gives 47=e5k\frac{4}{7} = e^{5k}. Taking the natural logarithm of both sides results in ln(47)=5k\ln\left(\frac{4}{7}\right) = 5k, so the decay rate is k=ln(4/7)5k = \frac{\ln(4/7)}{5}. To find the population after 24 hours, use this rate in the formula: A=700,000eln(4/7)524A = 700{,}000 e^{\frac{\ln(4/7)}{5} \cdot 24}. Evaluating this expression yields approximately 47,700. Thus, there will be about 47,700 bacteria remaining.

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Updated 2026-06-30

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