A puddle is in the form of a circle

Question

A puddle is in the form of a circle. If the puddle is evaporating in such a way that the are of the puddle is decreasing at a rate of 3 ft^2/sec at what rate is the radius decreasing when the radius of the puddle is 12 feet. Remember that the are S of a circle of radius r is S=(pi)r^2.

Answer 1

S = πr² Given dS/dt = -3. Find dr/dt when r = 12.

dS/dt = 2πr(dr/dt) -3 = 24π(dr/dt)

So, dr/dt = -1/(8π)

Answer 2

Since you know the A(rea) is πr²

dA/dt = 2πr dr/dt

You substitute the values to find the answer.

P.S. In the future it would be good practice to proofread your submission for accuracy and spelling!