Did you forget the denominator?
Your derivative is correct . . .The radius of a right circular cone is increasing at a rate of 5 in/sec
and its height is decreasing at a rate of 3 in/sec.
At what rate is the volume of the cone changing
when the radius is 50 inches and the height is 40 inches?
We have: .
We are given: .
Therefore: . in³/sec.