GMAT Quantitative Reasoning Practice Test 6

To find the area of the shaded region, you need the area of the inner circle subtracted from the outer circle. Since the formula for the area of a circle is A = πr2, you need to know at least the radius of each circle. Statement (1) gives you the area of the inner circle only, but no information about the outer circle. Statement (2) tells you the diameter of the outer circle is 20, so the radius is 10. Both statements are needed to answer the question.