Official Guide Explanation:
Data Sufficiency #140




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Solution and Metadata

Question: 140
Page: 285
Difficulty: 6 (Moderately Difficult)
Category 1: Geometry > Triangles > Special Tris
Category 2: Geometry > Triangles > Multiple figures

Explanation: To know the value of x + y, you need to know the value of each of the two variables. Statement (1) is insufficient, as it only pertains to the value of x. Statement (2) is also insufficient, as it provides no values for either variable.

Taken together, the statements are still insufficient. While we know the value of x, y remains unknown. Without the value of angle DAC or angle ACD, knowing that triangle ADC is isoceles isn't helpful. The correct choice is (E).

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