Deck 7: Extension G: Differential Equations
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Deck 7: Extension G: Differential Equations
1
Solve the initial-value problem.



2
A tank contains
L of brine with
kg of dissolved salt.Pure water enters the tank at a rate of
L/min.The solution is kept thoroughly mixed and drains from the tank at the same rate.How much salt is in the tank after
minutes?





3
A certain small country has $20 billion in paper currency in circulation,and each day $70 million comes into the country's banks.The government decides to introduce new currency by having the banks replace old bills with new ones whenever old currency comes into the banks.Let
denote the amount of new currency in circulation at time t with
Formulate and solve a mathematical model in the form of an initial-value problem that represents the "flow" of the new currency into circulation (in billions per day).



4
The Pacific halibut fishery has been modeled by the differential equation
where
is the biomass (the total mass of the members of the population)in kilograms at time t (measured in years),the carrying capacity is estimated to be
and
per year.If
,find the biomass a year later.





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5
One model for the spread of an epidemic is that the rate of spread is jointly proportional to the number of infected people and the number of uninfected people.In an isolated town of
inhabitants,
people have a disease at the beginning of the week and
have it at the end of the week.How long does it take for
of the population to be infected?
A)
B)
C)
D)
E)




A)

B)

C)

D)

E)

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6
Biologists stocked a lake with
fish and estimated the carrying capacity (the maximal population for the fish of that species in that lake)to be
The number of fish tripled in the first year.Assuming that the size of the fish population satisfies the logistic equation,find an expression for the size of the population after t years.


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7
Solve the differential equation. 
A)
B)
C)
D)
E) none of these

A)

B)

C)

D)

E) none of these
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8
Choose the differential equation corresponding to this direction field. 
A)
B)
C)
D)
E)

A)

B)

C)

D)

E)

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9
Solve the differential equation. 
A)
B)
C)
D)
E)

A)

B)

C)

D)

E)

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10
Find the solution of the differential equation
that satisfies the initial condition 


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