The radius of a spherical bubble is increasing at the rate of . At what rate is its volume increasing when the radius is ?

Answer and explanation

Correct answer: D.

  1. Step 1: Volume of a sphere is .
  2. Step 2: Differentiating with respect to time : .
  3. Step 3: Substitute and : .
Answer
.
Why not the others: uses instead of ; forgets to multiply by ; and divides by 4.

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