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A ripple's radius grows at 2 cm/s. How fast does its circumference grow?
A2 pi cm/s
B4 pi cm/s
C8 pi cm/s
D2 cm/s
Answer & Solution
Correct answer: B. 4 pi cm/s
C = 2 pi r gives dC/dt = 2 pi dr/dt = 4 pi cm/s whatever the radius.
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