Bunuel wrote:
In the figure above, what is the sum of the degree measures of the marked angles?
(1) The two overlapping triangles are equilateral.
(2) The two overlapping triangles have equal perimeters.
DS21268
Target question: What is the sum of the degree measures of the marked angles? Statement 1: The two overlapping triangles are equilateral. All three angles in an equilateral triangle are 60°
So are overlapping triangles look like this:
From here, if we let x and y represent the two marked angles, we get the following:
Now let's examine the
quadrilateral that exists in the intersection of the two triangles
Since angles in a triangle must add to 360°, we can write:
60° + x° + 60° + y° = 360°Simplify:
x° + y° + 120°= 360°Solve to get:
x° + y° = 240°In other words,
the sum of the marked angles = 240°Since we can answer the
target question with certainty, statement 1 is SUFFICIENT
Statement 2: The two overlapping triangles have equal perimeters.This information is not sufficient.
Consider these two possible cases:
Case a: The two triangles are identical equilateral triangles.
In this case, we get the same diagram we examined and statement 1:
Here, the answer to the target question is
the sum of the marked angles = 240°Case b: One triangle is an equilateral triangle, and the other is a 30-60-90 triangle with the same perimeter.
We get:
Since angles in a triangle must add to 360°, we can write:
30° + x° + 60° + y° = 360°Simplify:
x° + y° + 90°= 360°Solve to get:
x° + y° = 270°Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Answer: A
Cheers,
Brent