Chapter 8, Problem 26RE

Suppose that a room containing $\text{1200}{\text{ft}}^3$ of air is free of carbon monoxide. At time $t=0$ cigarette smoke containing $4\%$ carbon monoxide is introduced at the rate of $0.1{\text{ft}}^{\text{3}}/\text{min,}$ and the well-circulated mixture is vented from the room at the same rate.

(a) Find a formula for the percentage of carbon monoxide in the room at time $t.$

(b) Extended exposure to air containing $0.012\%$ carbon monoxide is considered dangerous. How long will it take to reach this level?