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Line ℓ lies in the xy-plane and does not pass through the origin. What is the slope of line ℓ...

GMAT Data Sufficiency : (DS) Questions

Source: Official Guide
Data Sufficiency
DS - Spatial Reasoning
HARD
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Notes
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Line ℓ lies in the xy-plane and does not pass through the origin. What is the slope of line ℓ ?

  1. The x-intercept of line ℓ is twice the y-intercept of line ℓ
  2. The x-and y-intercepts of line ℓ are both positive
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 need to find the slope of line \(\ell\) that lies in the \(xy\)-plane and does not pass through the origin.

Given Information:
- Line \(\ell\) lies in the \(xy\)-plane
- Line \(\ell\) does not pass through the origin \((0,0)\)

What We Need to Determine:
Can we find exactly ONE value for the slope of line \(\ell\)?

Key Insight: Since the line doesn't pass through the origin, it must have at least one intercept. To determine a unique slope, we need information that pins down the line to exactly one possibility.

Analyzing Statement 1

Statement 1: The x-intercept of line \(\ell\) is twice the y-intercept of line \(\ell\).

Let's think about what this relationship means:

When a line has both intercepts, it passes through two specific points on the axes. Statement 1 tells us these intercepts have a fixed ratio - the x-intercept is exactly twice the y-intercept.

Visualize it this way: If the y-intercept is at height 3, then the x-intercept must be at distance 6. If the y-intercept is at height 5, then the x-intercept must be at distance 10. No matter what value you choose for one intercept, the other is locked in by this \(2:1\) ratio.

This fixed ratio is like giving someone precise directions: "For every 1 unit up from the origin, go 2 units across." There's only one angle, one slope, that satisfies this requirement.

[STOP - Sufficient!]

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 x- and y-intercepts of line \(\ell\) are both positive.

This tells us the line crosses both axes in the positive region, but consider the possibilities:

Example 1: A steep line crossing at \((1, 0)\) and \((0, 10)\) - slope would be very negative
Example 2: A gentle line crossing at \((10, 0)\) and \((0, 1)\) - slope would be slightly negative
Example 3: A moderate line crossing at \((5, 0)\) and \((0, 5)\) - slope would be \(-1\)

All three lines satisfy "both intercepts are positive," yet each has a different slope. In fact, we can draw infinitely many lines connecting any point on the positive y-axis to any point on the positive x-axis.

Statement 2 is NOT sufficient.

This eliminates choices B and D.

The Answer: A

Statement 1 alone gives us a unique slope through the fixed ratio constraint, while Statement 2 alone allows infinitely many possible slopes.

Answer Choice A: "Statement 1 alone is sufficient, but Statement 2 alone is not 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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