
AP Calculus AB Scoring Guide
Unit 7 Progress Check: FRQ Part A
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1.
NO CALCULATOR IS ALLOWED FOR THIS QUESTION.
Show all of your work, even though the question may not explicitly remind you to do so. Clearly
label any functions, graphs, tables, or other objects that you use. Justifications require that you
give mathematical reasons, and that you verify the needed conditions under which relevant
theorems, properties, definitions, or tests are applied. Your work will be scored on the
correctness and completeness of your methods as well as your answers. Answers without
supporting work will usually not receive credit.
Unless otherwise specified, answers (numeric or algebraic) need not be simplified. If your
answer is given as a decimal approximation, it should be correct to three places after the
decimal point.
Unless otherwise specified, the domain of a function is assumed to be the set of all real
numbers for which is a real number.
A large vat is initially filled with a saltwater solution. A solution with a higher concentration of
salt flows into the vat, and solution flows out of the vat at the same rate. The number of pounds
of salt in the vat at time minutes is modeled by the function that satisfies the differential
equation . At time minutes, the vat contains 50 pounds of salt.
(a) Write an equation for the line tangent to the graph of at . Use the tangent line to
approximate the number of pounds of salt in the vat at time minutes.
Please respond on separate paper, following directions from your teacher.
(b) Show that satisfies the differential equation
with initial condition .
Please respond on separate paper, following directions from your teacher.
(c) The flow of solution into the vat is stopped, and the solution is drained. The depth of
solution in the vat is modeled by the function that satisfies the differential equation