A circle measuring 50 millimeters across lies inside a larger circle 150 millimeters across. The area between them is shaded.

Question

50 mm
150 mm

Answer 1

the shaded area is the difference between the two areas:

pi(150^2-50^2) = 20000pi mm^2

Answer 2

oops. Divide that by 4, since the sizes were diameters, not radii.

5000pi mm^2