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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

Source: Official Guide
Data Sufficiency
DS - Spatial Reasoning
HARD
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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 \(\mathrm{B + C}\)?

  1. \(\mathrm{A + 2B + C = 24}\)
  2. \(\mathrm{A + C = 18}\) and \(\mathrm{B = 3}\)
A
Statement (1) ALONE is sufficient but statement (2) ALONE is not sufficient.
B
Statement (2) ALONE is sufficient but statement (1) ALONE is not sufficient.
C
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D
EACH statement ALONE is sufficient.
E
Statements (1) and (2) TOGETHER are not sufficient.
Solution

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.

Answer Choices Explained
A
Statement (1) ALONE is sufficient but statement (2) ALONE is not sufficient.
B
Statement (2) ALONE is sufficient but statement (1) ALONE is not sufficient.
C
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D
EACH statement ALONE is sufficient.
E
Statements (1) and (2) TOGETHER are not sufficient.
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