Well, this question is only confusing most people, but it can't be any simpler than the difference of two circle. You can think x as the area shaded blue, y as the area shaded red, and z as the area intersected by those two circles. An simple question as x-y=? When you add z to both sides, it become what is the difference of the two circles whose radius is 15 and 20. The area of a circle is pi* r squared. That means the difference is 20 square*pi – 15 square*pi, in which is 400pi – 225pi, is 175pi. Approximating pi as 22/7, the answer would be 550. Or approximating pi a 3.14, the answer would be 549.5.
by Lyman Shen
