Hello, saxyliz!

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: .

Then: .

We are given: .

Therefore: . in³/sec.