The density of oil in a circular oil slick on the surface of the ocean at a distance of rmeters from the center of the slick is given by

p(r)=(100)/(1+r) kg/m^2

The shapes of the slices arethin rings with radiusrmeters, centered at the center of the oil slick because the oil slick is a circle

(a) Find an approximation for the mass of a slice.

(2(pi)r)(100/(1+r))dr

(b) Find the exact mass of oil when the radius of the slick is70meters.

Part a is correct, but part b is incorrect.