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The radius of a circular oil patch grows at 2 cm/s. How fast is its area increasing when the radius is 5 cm?
A20π cm^2/s
B5π cm^2/s
C10π cm^2/s
D25π cm^2/s
Answer & Solution
Correct answer: A. 20π cm^2/s
Area A = πr^2 gives dA/dt = 2πr(dr/dt) = 2π(5)(2) = 20π.
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