下面是GMAT频道整理的 2015年6月GMAT数学机经(六) ，欢迎阅读。

　　26 In the figure above, the diameter is 30, what is the area of shadow?

　　(1) Angle ACB = 60

　　(2) AB = 15

　　27 Is st < 0

　　(1) s^2t^3 < 0

　　(2) |s + t| < |s| + |t|

　　28 Is the quadrilateral ABCD a square

　　(1) AC = CD

　　(2) AC ⊥ CD

　　29 If O and D are centers of two circles, and arc AC is part of the circle D. What is the area of the shadow if AC is perpendicular with BD.

　　(1) AD = pi

　　(2) BD = 4

　　30 An aircraft flew from city P to city Q following the wind with 350 miles per hour, and return from city Q to city P with velocity 250 miles per hour. If the wind velocity between these two cities is constant and if the aircraft return from city Q immediately without landing, what is the average speed of the aircraft during this trip of 800 miles?