Official Guide Explanation:
Data Sufficiency #D28

Background

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Solution and Metadata

Question: D28
Page: 24
Difficulty: 5 (Moderate)
Category 1: Geometry > Triangles > other

Explanation: An isoceles triangle has at least two equal sides. To find the perimeter, we need to know the length of all three sides.

Statement (1) is insufficient. We need to know the lengths of the other two sides.

Statement (2) is also insufficient, for the same reason as (1).

Taken together, the statements are still insufficient. If two of the sides measure 16 and 20 and the triangle is isoceles, the third side must be either 16 or 20. We don't know which, though, and the two possibilities give us two different perimeters. Choice (E) is correct.

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