¡¡¡¡You can assume that a line that appears straight is straight and that angle
¡¡¡¡measures cannot be zero.
¡¡¡¡You can assume that the relative positions of points£¬ angles£¬ and objects ar
¡¡¡¡e as shown.
¡¡¡¡All drawings lie in a plane unless stated otherwise.
¡¡¡¡Example£º
¡¡¡¡In triangle ABC to the right£¬ what is the value of y£¿
¡¡¡¡£¨1£© AB = AC
¡¡¡¡£¨2£© x = 30
¡¡¡¡Explanation£º By statement £¨1£©£¬ triangle ABC is isosceles. Hence£¬ its base an
¡¡¡¡gles are equal£º y = z. Since the angle sum of a triangle is 180 degrees£¬ we
¡¡¡¡get x + y + z = 180. Replacing z with y in this equation and then simplifyin
¡¡¡¡g yields x + 2y = 180. Since statement £¨1£© does not give a value for x£¬ we c
¡¡¡¡annot determine the value of y from statement £¨1£© alone. By statement £¨2£©£¬ x
¡¡¡¡= 30. Hence£¬ x + y + z = 180 becomes 30 + y + z = 180£¬ or y + z = 150. Sinc
¡¡¡¡e statement £¨2£© does not give a value for z£¬ we cannot determine the value o
¡¡¡¡f y from statement £¨2£© alone. However£¬ using both statements in combination£¬
¡¡¡¡we can find both x and z and therefore y. Hence£¬ the answer is C.
¡¡¡¡Notice in the above example that the triangle appears to be a right triangle
¡¡¡¡¡¡ However£¬ that cannot be assumed£º angle A may be 89 degrees or 91 degrees£¬
¡¡¡¡we can't tell from the drawing. You must be very careful not to assume any m
¡¡¡¡ore than what is explicitly given in a Data Sufficiency problem.
¡¡¡¡ELIMINATION
¡¡¡¡Data Sufficiency questions provide fertile ground for elimination. In fact£¬
¡¡¡¡it is rare that you won't be able to eliminate some answer-choices. Remember
¡¡¡¡£¬ if you can eliminate at least one answer choice£¬ the odds of gaining point
¡¡¡¡s by guessing are in your favor.
¡¡¡¡The following table summarizes how elimination functions with Data Sufficien
¡¡¡¡cy problems.
