Suppose that a room containing 1300 cubic feet of air is originally free of carbon monoxide (CO). Beginning
at time t = 0, cigarette smoke containing 4% CO is introduced into the room at a rate of 0.8 cubic feet per
minute. The well-circulated smoke and air mixture is allowed to leave the room at the same rate.
Let A(t) represent the amount of CO in the room (in cubic feet) after t minutes.
(A) Write the DE model for the time rate of change of CO in the room. Also state the initial condition.
dA
dt
A(0)
(B) Solve the IVP to find the amount of CO in the room at any time t > 0.
A(t)
(C) Extended exposure to a CO concentration as low as 0.00012 is harmful to the human body. Find the time
at which this concentration is reached.
t=
minutes
Newton's Law of Cooling tells us that the rate of change of the temperature of an object is proportional to
the temperature difference between the object and its surroundings. This can be modeled by the
differential equation
dT
dt
k(TA), where T is the temperature of the object after t units of time
have passed, A is the ambient temperature of the object's surroundings, and k is a constant of
proportionality.
Suppose that a cup of coffee begins at 178 degrees and, after sitting in room temperature of 61 degrees
for 12 minutes, the coffee reaches 171 degrees. How long will it take before the coffee reaches 155
degrees?
Include at least 2 decimal places in your answer.
minutes
Decide whether each limit exists. If a limit exists, estimate its
value.
11. (a) lim f(x)
x-3
f(x) ↑
4
3-
2+
(b) lim f(x)
x―0
-2
0
X
1234
Elementary Statistics: Picturing the World (7th Edition)
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