In triangle ABC, point X is the midpoint of side AC and point Y is the midpoint of side BC....
GMAT Data Sufficiency : (DS) Questions
In \(\triangle \mathrm{ABC}\), point \(\mathrm{X}\) is the midpoint of side \(\mathrm{AC}\) and point \(\mathrm{Y}\) is the midpoint of side \(\mathrm{BC}\). If point \(\mathrm{R}\) is the midpoint of \(\overline{\mathrm{XC}}\) and if point \(\mathrm{S}\) is the midpoint of \(\overline{\mathrm{YC}}\), what is the area of \(\triangle \mathrm{RCS}\)?
- The area of \(\triangle \mathrm{ABX}\) is \(32\).
- The length of one of the altitudes of \(\triangle \mathrm{ABC}\) is \(8\).
Understanding the Question
We have triangle ABC with several midpoints creating smaller regions. Let's trace the relationships:
- X is the midpoint of AC, Y is the midpoint of BC
- R is the midpoint of XC (making R the \(\frac{3}{4}\) point of AC from A, or \(\frac{1}{4}\) point from C)
- S is the midpoint of YC (making S the \(\frac{3}{4}\) point of BC from B, or \(\frac{1}{4}\) point from C)
We need to determine: The area of triangle RCS
What "sufficient" means here: We can calculate the exact numerical value of the area of triangle RCS.
Key Insight
This is a classic geometry problem about area relationships through midpoints. When we connect midpoints in triangles, we create smaller triangles with predictable area ratios. Since R and S are "midpoints of midpoints," they're actually at the quarter-points of their respective sides from C. This creates a specific fractional relationship with the original triangle's area.
Analyzing Statement 1
Statement 1: The area of triangular region ABX is 32.
What Statement 1 Tells Us
Triangle ABX connects vertex B with the midpoint X of side AC. Here's the crucial relationship: when you connect a vertex to the midpoint of the opposite side, you create a triangle with exactly half the area of the original triangle.
Finding the Area of Triangle RCS
Since X is the midpoint of AC:
- Triangle ABX has half the area of triangle ABC
- Given: \(\mathrm{Area(ABX)} = 32\)
- Therefore: \(\mathrm{Area(ABC)} = 64\)
Now for triangle RCS:
- R is at the \(\frac{1}{4}\) point of AC from C
- S is at the \(\frac{1}{4}\) point of BC from C
- When both vertices are at quarter-points of their respective sides from a common vertex, the resulting triangle has area = \(\frac{1}{16}\) × Area of original triangle
Why \(\frac{1}{16}\)? Because:
- The base CR is \(\frac{1}{4}\) of the base CA
- The height from S to line CR is \(\frac{1}{4}\) of the corresponding height in triangle ABC
- Area factor = \(\frac{1}{4} \times \frac{1}{4} = \frac{1}{16}\)
Therefore: \(\mathrm{Area(RCS)} = \frac{64}{16} = 4\)
[STOP - Sufficient!] We found the exact area.
Statement 1 is sufficient.
This eliminates choices B, C, and E.
Analyzing Statement 2
Now let's forget Statement 1 completely and analyze Statement 2 independently.
Statement 2: The length of one of the altitudes of triangle ABC is 8.
What Statement 2 Provides
We know one altitude of triangle ABC equals 8, but we don't know:
- Which altitude it is (from which vertex?)
- The length of the corresponding base
- The overall shape or size of the triangle
Testing Different Scenarios
Since we don't know which base corresponds to the altitude of 8, let's test two different triangles:
Scenario 1: Altitude = 8, base = 10
- \(\mathrm{Area(ABC)} = \frac{1}{2} \times 10 \times 8 = 40\)
- \(\mathrm{Area(RCS)} = \frac{40}{16} = 2.5\)
Scenario 2: Altitude = 8, base = 20
- \(\mathrm{Area(ABC)} = \frac{1}{2} \times 20 \times 8 = 80\)
- \(\mathrm{Area(RCS)} = \frac{80}{16} = 5\)
Since different triangle configurations lead to different areas for RCS, we cannot determine a unique value.
Statement 2 is NOT sufficient.
This eliminates choices B and D.
The Answer: A
Statement 1 alone gives us the exact area of triangle RCS through geometric relationships, while Statement 2 leaves multiple possibilities open.
Answer Choice A: "Statement 1 alone is sufficient, but Statement 2 alone is not sufficient."