In the figure above, if A, B, and C are the areas, respectively, of the three nonoverlapping regions formed by...
GMAT Data Sufficiency : (DS) Questions
In the figure above, if A, B, and C are the areas, respectively, of the three nonoverlapping regions formed by the intersection of two circles of equal area, what is the value of \(\mathrm{B + C}\)?
- \(\mathrm{A + 2B + C = 24}\)
- \(\mathrm{A + C = 18}\) and \(\mathrm{B = 3}\)
Understanding the Question
We have two circles of equal area that overlap, creating three distinct regions: A, B, and C. Let's visualize this:
- Region A: The part of the first circle that doesn't overlap with the second
- Region B: The overlapping area (intersection of both circles)
- Region C: The part of the second circle that doesn't overlap with the first
Since both circles have equal total area, we can write:
- Area of Circle 1 = \(\mathrm{A + B}\)
- Area of Circle 2 = \(\mathrm{B + C}\)
Here's the key insight: Since these areas are equal, we have \(\mathrm{A + B = B + C}\), which simplifies to \(\mathrm{A = C}\).
Our goal is to find the specific value of \(\mathrm{B + C}\). For a statement to be sufficient, it must give us exactly one value for \(\mathrm{B + C}\).
Analyzing Statement 1
Statement 1: \(\mathrm{A + 2B + C = 24}\)
Since we know \(\mathrm{A = C}\), let's substitute:
- \(\mathrm{C + 2B + C = 24}\)
- \(\mathrm{2C + 2B = 24}\)
- \(\mathrm{2(B + C) = 24}\)
- \(\mathrm{B + C = 12}\)
We get a unique value: \(\mathrm{B + C = 12}\).
[STOP - 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: \(\mathrm{A + C = 18}\) and \(\mathrm{B = 3}\)
We know from our initial analysis that \(\mathrm{A = C}\). Using the first part:
- \(\mathrm{A + A = 18}\) (since \(\mathrm{A = C}\))
- \(\mathrm{2A = 18}\)
- \(\mathrm{A = 9}\)
Therefore, \(\mathrm{C = 9}\) as well.
With \(\mathrm{B = 3}\) and \(\mathrm{C = 9}\):
- \(\mathrm{B + C = 3 + 9 = 12}\)
We get a unique value: \(\mathrm{B + C = 12}\).
[STOP - Sufficient!]
This eliminates choice A.
The Answer
Both statements independently give us \(\mathrm{B + C = 12}\).
Answer: D - Each statement alone is sufficient.