Calculus Question, approximating errors?

Question

The radius of a sphere is found to be 20 centimeters. The possible error in its measurement is 0.25 centimeters. Use differentials to compute (a) the possible error in computing the surface area of the sphere, and (b) the relative error in computing the surface area. (Formula is S=(4)(pi)(r2)

Answer 1

Apply derivative with respect of r.

In this case r = 20 and dr = 0.25

a) Possible error

b) Relative error