A water tank has been contaminated with salt and must be flushed with pure water. The concentration of salt in the tank is given by the equation $y=.1+3.02 e^{-.4 t}$, where $y$ is the concentration of salt in milligrams per gallon and $t$ is the time, in hours, since flushing began. Match each question with one of the solutions $\mathrm{A}, \mathrm{B}, \mathrm{C}$, or $\mathrm{D}$.
-How long will it take for the concentration to reach $2 \mathrm{mg} / \mathrm{gal}$ ?
A) Evaluate $.1+3.02 e^{-.4(1 / 2)}$
B) Solve $\frac{1}{2}(3.12)=.1+3.02 e^{-.4 t}$
C) Evaluate $.1+3.02 e^{-.4(2)}$
D) Solve $2=.1+3.02 e^{-.4 t}$

Question

Quizplus · Accepted Answer

To find the time it takes for the concentration to reach 2 mg/gal, we need to solve the equation for $t$ when $y = 2$. This is directly represented by option D, where $2 = .1 + 3.02e^{-.4t}$.

A Water Tank Has Been Contaminated with Salt and Must y=.1+3.02e−.4ty=.1+3.02 e^{-.4 t}y=.1+3.02e−.4t

A Water Tank Has Been Contaminated with Salt and Must $y=.1+3.02 e^{-.4 t}$