College Algebra & Trigonometry, 2018a

3.1. EXPONENTIAL AND LOGISTIC APPLICATIONS 149
Example
If a patient is injected with 150 micrograms of medication, the amount of medication
still in the bloodstream after t hours is given by the function:
A(t) =150e −0.12t
a) Find the amount of medication in the bloodstream after 3 hours.
Round your answer to the nearest 100th.
b) How long will it take for the amount of medication to reach 60 micrograms?
Round your answer to the nearest 10th of an hour.
In this section we will focus on solving these problems using the graphing calculator.
In later sections, we will cover processes that can be used to solve these
problems algebraically. It is helpful to understand both methods of solution.
First, let’s graph the function given in the problem:
150
100
50
y = 150e −0.12x
5 10 15 20
We can directly calculate the answer for part (a) by plugging the value of 3 for t
or we can use the table in the graphing calculator to find this value: